INTRODUCTION — Large, prospective epidemiologic studies of diet and chronic diseases have facilitated major advances in our understanding of the contribution of diet to the pathogenesis of disease [1]. These studies are complemented by randomized trials and studies of nutrient action in animal models, which have led to changing dietary guidelines around the world [2]. Although guidelines vary from country to country, recommendations from different parts of the world share similarities in terms of the emphasis on certain types of foods and nutrients [2-6].

This topic will discuss the important components of a healthy diet. In addition, this review focuses only on the direct effects of the consumption of certain nutrients on health without considering the larger environmental impacts of food choices and dietary patterns.

Dietary assessment and diets for specific populations are discussed elsewhere. (See "Dietary assessment in adults" and "Dietary recommendations for toddlers, preschool, and school-age children" and "Obesity in adults: Dietary therapy" and "Geriatric nutrition: Nutritional issues in older adults".)

CALORIC BALANCE — Maintaining caloric balance over time is important to maintaining healthy weight. Overnutrition leading to overweight and obesity is the single most important dietary factor associated with poor health outcomes. It is associated with premature mortality as well as increased incidence of cardiovascular disease (CVD), diabetes, hypertension, cancer, and other important conditions [7-9]. (See "Overweight and obesity in adults: Health consequences".)

For patients with normal weight, caloric intake should equal energy expenditure. Balancing caloric intake requires that many individuals limit their typical calorie consumption, while also engaging in physical activity. (See "The benefits and risks of aerobic exercise".)

Calculating total energy expenditure for recommended daily caloric intake is based on age, sex, weight, and activity level (table 1). Calculating one's actual daily caloric intake can be aided by using 24-hour dietary recall, a food diary, or other assessment tools to determine caloric intake of different foods and beverages. Assessment tools, including consumer-focused apps and online tools that can help patients readily track what they eat and drink, are discussed separately. (See "Dietary assessment in adults", section on 'Assessment tools'.)

MACRONUTRIENTS — Macronutrients are the chemical compounds consumed in the largest quantities and provide bulk energy. The three primary macronutrients include carbohydrates, proteins, and fats. Fiber can also be considered a macronutrient [6].

Carbohydrate — Carbohydrates should make up 45 to 65 percent of total caloric intake, as recommended by the United States Dietary Guidelines [6]. Both the quantity and type of carbohydrate (eg, whole-grain versus refined-grain) have differential effects on postprandial glucose levels and glycemic index. Several prospective studies have associated diets high in glycemic index with risk of developing type 2 diabetes mellitus, coronary heart disease, and some cancers. Glycemic index for common foods are available in the table (table 2). One important way of achieving a healthy diet is to replace carbohydrates having a high glycemic index (eg, white rice, pancakes) with a low glycemic index (eg, fruits, vegetables).

Added sugars should be limited and comprise no more than 10 percent of total calories consumed [6]. These sugars often come from sweetened beverages and almost all processed foods. If a large percentage of calories comes from added sugars, it may be difficult for patients to meet their nutritional needs within caloric limits. Naturally occurring sugars (eg, from fruit or milk) are not considered added sugars. However, fruit juice should still be limited to small daily amounts, if any, as it tends to be high in calories without the added benefit of fiber, which is found in whole fruit. (See "Dietary carbohydrates" and 'Sweetened beverages' below.)

Protein — Protein should make up 10 to 35 percent of total caloric intake, as recommended by the United States Dietary Guidelines [6]. Individuals should be counseled to eat a variety of healthy protein-rich foods, including fish, lean meat, poultry, eggs, beans, peas, soy products, and unsalted nuts and seeds. Patients should be advised to avoid protein sources with unhealthy fats. (See "Dietary fat", section on 'Recommendations for patients'.)

Common sources of dietary protein include whole foods (eg, meat, fish, egg, vegetables, milk) and protein powders (eg, casein, whey, soy). The source of protein has a differential effect on health (eg, red meats are associated with modestly increased mortality compared with white meats). (See 'Protein-rich foods' below.)

Fat — Fat should make up 20 to 35 percent of total caloric intake, as recommended by the United States Dietary Guidelines [6]. The type of fat consumed appears to be more important than the amount of total fat (table 3). Trans fats contribute to coronary heart disease (CHD), while n-3 (and perhaps n-6) polyunsaturated fats are protective [10,11]. (See "Dietary fat", section on 'Quality of fat'.)

Trans fatty acid consumption should be kept as low as possible. The major sources of trans fats include margarines and partially hydrogenated vegetable fats. These fats are also present in many processed and fast foods. The United States Dietary Guidelines recommend limiting dietary cholesterol and keeping consumption of saturated fat under 10 percent of calories per day [6].

There is some evidence that long-term consumption of fish oil and n-3 fatty acids reduces the risk of cardiovascular disease (CVD). One to two servings of oily fish in the weekly diet is suggested for most adult patients. This is discussed in detail separately. (See "Overview of primary prevention of cardiovascular disease", section on 'Omega-3 fatty acids'.)

Consumption of trans fat, saturated fat, and dietary cholesterol each affect plasma cholesterol levels. Elevated plasma cholesterol concentrations, particularly low-density lipoprotein (LDL) cholesterol, show a strong and consistent association with the incidence of CHD [12,13]. However, there are limited data showing that dietary interventions to lower cholesterol intake improve patient outcomes. (See "Lipid management with diet or dietary supplements" and "Lipoprotein(a)".)

Fiber — The recommended amount of dietary fiber is 14 g per 1000 calories [6]. For most moderately active adults in the United States, that translates to approximately 25 g to 36 g per day.

Fiber is the portion of plants that cannot be digested by enzymes in the gastrointestinal tract. Fiber is available in a large variety of natural foods and supplements (table 4). Patients should be advised to replace refined grains (eg, white rice, white bread) with whole grains (eg, brown rice, whole-wheat bread), which have higher fiber content. (See 'Grains' below.)

Increased fiber intake is associated with many health benefits, including a decreased risk of coronary heart disease (CHD), cardiovascular and all-cause mortality, colorectal cancer, stroke, and type 2 diabetes [14-21]. High fiber diets may in part protect against CHD by controlling cardiovascular risk factors, including lowering insulin levels and blood pressure, and improving lipid profiles [22,23].

High fiber intake is associated with a 24 to 38 percent reduction in the risk of CHD and stroke compared with low fiber intake [15-19]. In addition, fiber derived from grain rather than from fruit or other sources, is more strongly associated with the observed benefit.

There is a dose response relationship, with increasing amounts of fiber intake associated with greater reduction in risk of CVD. As an example, in a 2014 meta-analysis of seven prospective cohort studies including over 900,000 patients, high fiber intake was associated with decreased mortality (RR 0.77, 95% CI 0.74-0.80), and each 10 g per day increment in fiber intake was associated with an additional reduction in risk (RR 0.89, 95% CI 0.85-0.92) [24]. Similarly, in a pooled analysis of 10 prospective cohort studies including 330,000 participants, each 10 g per day increase in intake of fiber per day was associated with a 14 percent reduction in the risk of coronary events and a 27 percent reduction in CHD death [25].

The benefit is also observed in people with established CVD. For example, in a prospective cohort study following 4000 patients after a first myocardial infarction (MI), eating a high-fiber diet post-MI was associated with lower cardiovascular (RR 0.72, 95% CI 0.52-0.99) and all-cause (RR 0.73, 95% 0.58-0.91) mortality [26]. The largest benefit was seen among those with the greatest increase in fiber consumption, comparing pre- and post-MI fiber intake.

The consumption of fiber derived from grains has a protective effect against the development of type 2 diabetes mellitus. In addition, increased fiber intake may also be beneficial in controlling blood glucose in patients with established diabetes. (See "Type 2 diabetes mellitus: Prevalence and risk factors", section on 'Dietary patterns' and "Nutritional considerations in type 1 diabetes mellitus" and "Nutritional considerations in type 2 diabetes mellitus".)

Fiber intake reduces the risk of colorectal cancer [14,27]. Dietary fiber and risk of colorectal and other cancers is discussed separately. (See "Colorectal cancer: Epidemiology, risk factors, and protective factors", section on 'Fiber' and "Overview of cancer prevention", section on 'Fruits and vegetables'.)

MICRONUTRIENTS — Nutrients needed in very small amounts are called micronutrients and include several minerals (eg, sodium, calcium) and vitamins. (See "Overview of dietary trace elements" and "Vitamin supplementation in disease prevention".)

Sodium — The recommended dietary sodium intake for the general population is less than 2300 mg per day [6].

A high dietary intake of sodium is associated with the development of hypertension and cardiovascular disease (CVD). Regular consumption of salt-preserved foods (eg salted/dried fish and pickled vegetables) may increase the risk of stomach cancer [28]. (See "Risk factors for gastric cancer", section on 'Salt and salt-preserved foods'.)

Reduction in sodium intake is associated with decreased risk of cardiovascular events, including death [29]. Some individuals are particularly sensitive to sodium in the diet (eg, older individuals, African Americans, patients with chronic kidney disease) and are referred to as being sodium-sensitive. Sodium restriction is discussed in detail separately. (See "Salt intake, salt restriction, and primary (essential) hypertension".)

Calcium and vitamin D — Recommended calcium intake is 1200 mg for postmenopausal women and 1000 mg for other individuals; recommended vitamin D intake is 600 international units (IU) daily (or 800 IU daily if aged 70 years or older) (table 5) [30]. (See "Prevention of osteoporosis", section on 'Calcium and vitamin D'.)

Calcium and vitamin D are necessary for normal skeletal homeostasis. Given the benefits of calcium and vitamin D in preventing osteoporosis, patients should be encouraged to consume foods with calcium and/or vitamin D, such as fortified milk products. Supplements should be offered to patients with inadequate calcium or vitamin D intake. Recommendations for calcium and vitamin D supplementation in the treatment of osteoporosis are discussed elsewhere. (See "Calcium and vitamin D supplementation in osteoporosis".)

While the effect of calcium and vitamin D intake on most extraskeletal health outcomes remains unclear, good evidence shows that calcium supplementation likely lowers the risk of colorectal cancer [27]. This is discussed in detail separately. (See "Vitamin D and extraskeletal health" and "Risk factors for prostate cancer", section on 'Calcium and vitamin D' and "Colorectal cancer: Epidemiology, risk factors, and protective factors", section on 'Calcium and dairy products' and "Kidney stones in adults: Epidemiology and risk factors" and "Overview of cancer prevention", section on 'Calcium' and "Overview of cancer prevention", section on 'Vitamin D'.)

Folate — In addition to its importance for erythropoiesis, folate has an important role in the prevention of neural tube defects. It is not clear if folate prevents other diseases (see "Vitamin supplementation in disease prevention", section on 'Folic acid'):

●Low folate intake is associated with an increased risk of neural tube defects; supplementation with folic acid reduces this risk in women [31]. Women of reproductive potential should take a daily multivitamin containing at least 0.4 mg of folic acid. (See "Folic acid supplementation in pregnancy".)

●In observational studies, higher dietary folate intake is associated with a decreased risk of developing colon cancer [32-34]. However, in randomized trials, folic acid supplementation does not seem to protect against cancer and may increase risk of colorectal and other cancers [35,36]. (See "Colorectal cancer: Epidemiology, risk factors, and protective factors" and "Vitamin supplementation in disease prevention".)

Other vitamins — Recommended dietary allowances for the major vitamins are presented in the table (table 6). Vitamin supplementation is discussed in detail separately. (See "Vitamin supplementation in disease prevention".)

TYPES OF FOOD — In addition to macronutrients and micronutrients, specific types of food intake play an important role in nutrition and health outcomes. As an example, in large, prospective cohort studies of healthy men and women, fruits, vegetables, and nuts were associated with weight loss whereas processed meats, unprocessed red meats, potato chips, fried foods, and desserts were associated with weight gain [37].

Despite variability in how types of food are classified, many countries categorize food into the following groups: fruits, vegetables, grains, dairy products, and meat/protein-rich foods [3-5,38]. The United States Dietary Guidelines provide a guide to recommended average daily intake of food groups based on caloric intake (table 7).

Fruits and vegetables — Patients should be counseled to consume 2.5 servings of vegetables and 2 servings of fruits daily for a 2000-calorie diet (table 7) [6]. Fruits and vegetables are a rich source of fiber and essential vitamins and minerals, as well as carbohydrates with a low glycemic index. (See 'Fiber' above and "Vitamin supplementation in disease prevention" and "Dietary carbohydrates", section on 'Glycemic index'.)

Increased fruit and vegetable intake is associated with decreased risk for mortality, cardiovascular disease (CVD), and some cancers.

Mortality — Large, prospective cohort studies have found that increased consumption of fruits and vegetables is associated with decreased all-cause and coronary heart disease (CHD) mortality [39-42]. A 2014 systematic review and meta-analysis of 16 prospective cohort studies that reported risk estimates for all-cause, cardiovascular, and cancer mortality found that each serving of fruit and vegetables (up to five servings a day) was associated with a lower risk of all-cause mortality [43]. There was no association with risk of cancer mortality. In the European Prospective Investigation into Cancer and Nutrition (EPIC) study, compared with those consuming less than three portions of fruits and vegetables a day, participants consuming eight or more portions had a lower risk of CHD mortality [42]. Both the 2014 meta-analysis and the EPIC study found that each serving was associated with an approximate 4 percent lower risk of CHD mortality [42,43].

Cardiovascular disease — Several studies suggest that fruit and vegetable consumption is associated with a lower risk of CHD and stroke [44-46]. A meta-analysis of cohort studies also found higher intake of fruits and vegetables was associated with a lower risk of stroke; compared with intake below three servings per day, risk was reduced with three to five servings and with more than five servings daily (relative risk [RR] 0.89 and 0.74, respectively) [47]. One study found that the lowest risks were associated with high consumption of cruciferous vegetables (eg, broccoli, cabbage, cauliflower, Brussels sprouts), green leafy vegetables, citrus fruits, and vitamin C-rich fruits and vegetables [48]. Intake beyond six servings per day provided little further reduction in ischemic stroke risk compared with intake of five to six servings per day. Another prospective cohort study of over 450,000 adults aged 30 to 79 years in China found that compared with little or no fresh fruit consumption, those who ate fresh fruit daily had decreased risk for cardiovascular death (hazard ratio [HR] 0.6, 95% CI 0.54-0.67), major coronary events (HR 0.66, 95% CI 0.58-0.75), ischemic stroke (HR 0.75, 95% CI 0.72-0.79), and hemorrhagic stroke (HR 0.64, 95% CI 0.56-0.74) [46]. There was a dose-response relationship between each outcome and the amount of fresh fruit consumed. Additionally, fresh fruit consumption was associated with decreased blood pressure and blood glucose levels.

A possible explanation for this association is the high content of fiber in these foods, which may offer substantial protection against heart disease and stroke. (See 'Fiber' above.)

Cancer — Large prospective cohort studies have not found a substantial effect of fruits and vegetables on cancer incidence in the general population. However, there is evidence of impact on some specific cancers. A higher intake of fruits and vegetables likely lowers the risk of aerodigestive cancers [27]. The Pooling Project of Prospective Studies of Diet and Cancer has found an association between an increased intake of fruits and vegetables and a lower risk of estrogen receptor-negative breast cancer. Some observational studies support an association between higher intake of tomatoes and tomato-based products with a lower risk of prostate cancer [49,50]. (See "Overview of cancer prevention", section on 'Fruits and vegetables'.)

Grains — Individuals should consume at least one-half of all grains as whole grains (ie, three or more ounces of whole grain for a 2000-calorie diet), as recommended by the United States Dietary Guidelines (table 7) [6], and replace refined grains with whole grains wherever possible.

Foods made from wheat, oats, rice, cornmeal, or barley are all grain products. Common types of food made from grain include breads, breakfast cereals, oatmeal, tortillas, and pasta. Grain products vary by level of milling, or processing, and can be defined as follows:

●Refined grains (eg, white rice, white bread, refined and sweetened cereals) have bran and germ removed during processing, which also removes fiber, iron, B vitamins, and other nutrients. Processing produces a finer texture and improves shelf life.

●Enriched grains are refined grains that have iron and B vitamins added back, but not fiber in most cases.

●Whole-grain foods include brown rice, whole-wheat bread, whole-grain cereal, and oatmeal. These are a good source of fiber and other nutrients and are considered carbohydrates with a lower glycemic index.

Increased consumption of whole grains is associated with a variety of health benefits, including improved weight management, reduction in cardiovascular and all-cause mortality, and decreased incidence of coronary heart disease (CHD) and cancer [14,37,51,52]. Representative studies include:

●In a prospective study of over 120,000 healthy individuals, an increased intake in refined grains was associated with long-term weight gain, whereas an increased intake in whole grains was associated with weight loss [37].

●In a 2014 meta-analysis of 18 studies including over 400,000 participants, increased whole-grain intake was associated with decreased risk for CHD (RR 0.79, 95% CI 0.74-0.83) [51].

●In a pooled prospective cohort study including over 117,000 individuals, higher whole-grain consumption was associated with lower cardiovascular (RR 0.85, 95% CI 0.78-0.92) and total (RR 0.91, 95% CI 0.88-0.95) mortality [52].

The World Cancer Research Fund/American Institute for Cancer Research, in their Third Expert Report: Diet, Nutrition, Physical Activity and Cancer, recommends increased dietary intake of whole grains to reduce the risk of developing colorectal cancer [27].

Dairy — The United States Dietary Guidelines recommend that individuals include three cups of dairy products daily for a 2000-calorie diet (table 7) [6]. The dairy food group is composed of milk and foods made from milk. Examples include milk, cheese, yogurt, and milk-based desserts (eg, pudding, frozen yogurt, ice cream). Dairy products are a good source of protein, calcium, vitamin D, and potassium. Diets that include lower amounts of dairy products should ensure adequate intake of these nutrients from other sources.

Intake of dairy products likely lowers the risk of colorectal cancer [27]. In addition, dairy consumption may reduce the risk of CVD [53-55]:

●One meta-analysis of 10 cohort studies found that milk drinking may be associated with a small reduction in heart disease (RR 0.87, 95% CI 0.74-1.03) and/or ischemic stroke (RR 0.84, 95%CI 0.78-0.90) [53].

●In a subsequent large, prospective cohort study, 136,000 people from 21 low- and middle-income countries where dairy consumption is generally low were followed for a median of approximately nine years [55]. Consumption of higher amounts of dairy (more than two servings per day versus no intake) was associated with a reduction in total mortality (HR 0.83, 95%CI 0.72-0.96), major CVD (HR 0.78, 95% CI 0.67-0.90), and stroke (HR 0.66, 0.53-0.82).

Protein-rich foods — Individuals should be advised to take 5.5 ounces of protein-rich foods daily (approximately two to three servings) for a 2000-calorie diet, as recommended by the United States Dietary Guidelines (table 7) [6]. Healthy protein-rich foods include seafood, poultry, beans, peas, nuts, and seeds. (See 'Protein' above and 'Fat' above.)

●Red and processed meat – Increased consumption of red and processed meat is consistently associated with a small to moderate increased risk of numerous chronic diseases and premature mortality [56]. Although modest, and unconfirmed by randomized trials, these risks are potentially important given the high level of red meat consumption in the United States and increasing consumption of red meat globally. As examples, in meta-analyses and pooled analyses of prospective cohort studies, increased consumption of red and processed meat are associated with an increased risk of type 2 diabetes [57], stroke [58], colorectal cancer [59], and increased CVD mortality [60]. In addition, in similar studies, increased intake of processed meat is associated with increased risks of coronary heart disease [60,61] and all-cause mortality [62,63].

In 2019, dietary recommendations proposed by the Nutritional Recommendations Consortium (NutriRECS) indicate that a recommendation for adults to reduce their current red and processed meat consumption is not supported by their analysis [64]. This is a weak recommendation, however, based upon the impact of a reduction in meat consumption of three servings of unspecified size per week. In addition, the recommendation was based upon the results of four meta-analyses showing low-certainty evidence of the small health effects of red and processed meat consumption [65-68], as well as a systematic review evaluating consumer values and preferences [69]. It is unclear where these recommendations should fit in relation to those of multiple other dietary guidelines that support limiting consumption of red and processed meat [70,71]. While the results of their meta-analyses are similar to others, their use of the GRADE system, which classifies observational data as low-quality evidence, remains a point of contention. (See "Overview of clinical practice guidelines", section on 'Grading guidelines' and "Evidence-based medicine", section on 'Categories of evidence' and "Overview of clinical practice guidelines", section on 'Disagreement among guidelines'.)

Of note, the International Agency for Research on Cancer classifies processed meat as a Group 1 human carcinogen [71]. (See "Colorectal cancer: Epidemiology, risk factors, and protective factors", section on 'Red and processed meat'.)

●Fish – One to two servings of oily fish per week is suggested for most adults. In a 2014 meta-analysis of 11 prospective cohort studies, fish consumption ≥4 times a week was associated with a decreased risk of acute coronary syndrome (RR 0.79, 95% CI 0.70-0.89) with a dose-response relationship (each additional 100 g serving/week associated with RR 0.95, 95% CI 0.92-0.97) [72].

There is some evidence that long-term consumption of fish oil and omega-3 fatty acids reduces the risk of CVD. Compared with supplements, however, consumption of fish also provides potentially beneficial protein, vitamins, and minerals [73]. Thus, for many individuals, regular dietary seafood consumption can be considered the optimal method to obtain n-3 polyunsaturated fatty acids (n-3 PUFA) (table 8). Fish oil is discussed in detail elsewhere. (See "Fish oil: Physiologic effects and administration".)

●Nuts – Nut consumption is associated with lower risk for CVD. As an example, a study that combined data from three large cohorts found that the risk of myocardial infarction or stroke was reduced among participants who consumed nuts five or more times per week compared with participants who rarely ate nuts (HR 0.86, 95% CI 0.79-0.93) [74]. Peanuts, tree nuts, and walnuts were all associated with similar reductions in the risk of CVD.

BEVERAGES

Alcohol — If alcohol is consumed, it should only be consumed in moderation, with no more than one drink per day for women and two drinks per day for men [6]. The specific risks and benefits of alcohol consumption vary based on age, sex, and comorbid conditions. Generally, moderate consumption in most older adults can lower the risk of cardiovascular disease (CVD) (see "Cardiovascular benefits and risks of moderate alcohol consumption"). However, low-level consumption can increase the risk of breast cancer and moderate or higher intake can increase the risk of other cancers, including colon cancer. Those that drink moderately likely do not need to be counseled to stop. At the same time, those who do not drink alcohol do not need to start. Alcohol is discussed in detail separately.

Sweetened beverages — The consumption of soft drinks and other sweetened beverages (eg, fruit drinks, sports drinks, and energy drinks) should be discouraged [6]. These beverages are a major source of added refined sugar and calories in the diet. (See 'Carbohydrate' above.)

Sugar-sweetened beverages are a key contributor to weight gain and obesity [27]. Their consumption is also associated with lower intake of key nutrients because they are consumed instead of nutrient-dense foods. In addition to excess weight, intake of sugar-sweetened beverages has been found to increase the risk of coronary heart disease (CHD), type 2 diabetes, hypertension, and metabolic syndrome [75-80]. Individuals should be encouraged to drink plain water rather than sweetened beverages.

Coffee — Coffee intake likely lowers the risk of liver and uterine cancers [27], and the United States Dietary Guidelines state that "moderate coffee consumption (three to five 8 oz cups/day or providing up to 400 mg/day of caffeine) can be incorporated into healthy eating patterns" [6]. The risks and benefits of caffeine are discussed separately. (See "Benefits and risks of caffeine and caffeinated beverages".)

TYPES OF DIET — Many different types of diets have been evaluated for their overall health effects, including impact on cardiovascular disease, diabetes, hypertension, cancer, and mortality. In addition, several types of diets have been studied for effects on weight reduction, including low-calorie, low-fat, low-carbohydrate, high-protein, and portion-controlled diets. These diets are discussed in detail separately. (See "Obesity in adults: Dietary therapy", section on 'Types of diets'.)

Outside of overweight and obese populations, there are few well-designed prospective cohort studies or randomized trials comparing different diets. This is partly due to the wide variability in cultural influences on dietary patterns. It is not known which type of diet is optimal for the general population.

The World Health Organization (WHO) recommendations for a healthy diet emphasize limiting the intake of saturated and trans fatty acids, free sugars, and salt, while increasing the intake of fruits, vegetables, legumes, nuts, and whole grains [81]. Observational data from large cohorts support these recommendations:

●A 2014 meta-analysis of 11 cohort studies in older adults in Europe and the United States found that higher adherence to the WHO dietary guidelines was associated with increased life expectancy [82].

●A subsequent large cohort study examined the association of dietary modifications made by individuals during a 12-year period with all-cause mortality during the next 12 years [83]. Those who improved their diet quality, which was assessed using the Alternative Healthy Eating Index-2010 score, the Alternative Mediterranean Diet score, or the Dietary Approaches to Stop Hypertension (DASH) score, had a significantly lower all-cause mortality compared with individuals who did not change their diet (relative risk reductions ranging from 9 to 16 percent). Participants who maintained a high-quality diet over the 12-year period had the lowest mortality.

A low-fat diet, vegetarian diet, DASH diet, and the Mediterranean diet are among the most commonly used diets to maintain good health, where weight loss is not necessarily the primary goal. All of these diets are associated with health benefits. The decision to choose one of these diets is generally based on patient preference and the ability to adhere to a given diet.

Low-fat diet — Low-fat diets are considered one of the standard strategies to help patients lose or maintain weight. This is discussed in detail separately. (See "Obesity in adults: Dietary therapy", section on 'Low-fat diets'.)

Low-fat diets may lead to weight loss even in patients who do not intend to lose weight. A systematic review and meta-analysis of 30 randomized trials in adults with no intention to lose weight found that compared with a usual diet, a low-fat diet was associated with weight loss (mean weight reduction 1.5 kg, 95% CI -2.0 to -1.1 kg) [84]. More fat reduction was associated with more weight loss.

Low-cholesterol diet — While elevated levels of low-density (LDL) cholesterol are an established risk factor for the development of CVD, the relationship between dietary cholesterol intake and CVD is less certain. As examples:

●In a prospective cohort study (using pooled data from six studies in the United States), over 29,000 adults without CVD at baseline were followed for a median of 17.5 years, diet data assessed, and outcomes measured [85]. Each additional 300 mg of dietary cholesterol consumed per day was associated with a moderately increased risk of CVD (hazard ratio [HR] 1.17; 95% CI, 1.09-1.26) and all-cause mortality (HR 1.18; 95% CI, 1.10-1.26). Egg consumption was not independently associated with this increased risk.

●In an earlier prospective cohort study (using pooled data from two United States studies), over 117,000 adults without preexisting CVD were followed for 14 years, egg consumption determined, and incidence of CVD (coronary heart disease [CHD] and stroke) assessed [86]. There was no association between egg consumption and the risk of CVD, even among those consuming more than seven eggs per week. Among male diabetic participants consuming seven or more eggs per week had an increased risk of developing CVD compared with those who ate less than one egg per week (relative risk [RR] 2.02; 95% CI, 1.05 to 3.87).

Although the 2015 to 2020 Dietary Guidelines for Americans no longer recommend limiting daily dietary cholesterol consumption to 300 mg or less, they advise maintaining an overall healthy eating pattern and consuming as little dietary cholesterol as possible [87].

Vegetarian diet — Vegetarian diets vary considerably depending on the degree of dietary restrictions [88]. According to the strictest definition, a vegetarian diet consists primarily of cereals, fruits, vegetables, legumes, and nuts; animal foods, including milk, dairy products, and eggs generally are excluded [89,90]. Several less restrictive vegetarian diets may include eggs and dairy products. Some vegetarian diets may be grouped as follows:

●Macrobiotic – Vegetables, fruits, legumes, and seaweeds are included in the diet, while whole grains, especially brown rice, are also emphasized. Locally-grown fruits are recommended. Animal foods limited to white meat or white meat fish may be included in the diet once or twice a week.

●Semi-vegetarian – Meat occasionally is included in the diet. Some people who follow such a diet may not eat red meat but may eat fish and perhaps chicken.

●Lacto-ovovegetarian – Eggs, milk, and milk products (lacto = dairy; ovo = eggs) are included, but no meat is consumed.

●Lactovegetarian – Milk and milk products are included in the diet, but no eggs or meat are consumed.

●Vegan – All animal products, including eggs, milk, and milk products, are excluded from the diet. Some vegans do not use honey and may refrain from using animal products such as leather or wool. They also may avoid foods that are processed or not organically grown [91].

The long-term effects of a vegetarian diet on health outcomes are difficult to separate from lifestyle elements associated with a vegetarian diet (eg, regular exercise, avoidance of tobacco and alcohol products). However, observational studies suggest that consumption of a vegetarian diet is associated with lower incidence of obesity, CHD, hypertension, type 2 diabetes, and certain cancers [92-95]. Results of randomized trials have found a beneficial impact of vegetarian diets on a number of cardiovascular risk factors [96].

The nutritional adequacy of a vegetarian diet should be judged individually, not on the basis of what it is called, but on the type, amount, and variety of nutrients that are consumed [97]. Vegans, who typically exclude dairy products in their diet, may have low bone mineral density and higher risk of fractures due to inadequate intake of calcium [98]. Patients on a vegetarian diet who completely exclude animal products may also have inadequate vitamin B12 intake and may need to take vitamin B12 supplements. (See "Vitamin supplementation in disease prevention", section on 'Special diets'.)

DASH diet — The DASH diet is comprised of four to five servings of fruit, four to five servings of vegetables, two to three servings of low-fat dairy per day, and <25 percent dietary intake from fat.

The DASH diet has been studied in both normotensive and hypertensive populations and found to lower systolic and diastolic pressure more than a diet rich in fruits and vegetables alone [99]. The combination of low-sodium and DASH diet resulted in further decreases in blood pressure, comparable with those observed with antihypertensive agents [100]. (See "Salt intake, salt restriction, and primary (essential) hypertension" and "Diet in the treatment and prevention of hypertension".)

The DASH diet has also been associated with a lower risk of colorectal cancer, cardiovascular disease (CVD), premature mortality, and gout (in men) [101-106]. (See "Lifestyle modification and other strategies to reduce the risk of gout flares and progression of gout", section on 'Dietary composition'.)

Mediterranean diet — There is no single definition of a Mediterranean diet, but such a diet is typically high in fruits, vegetables, whole grains, beans, nuts, and seeds, includes olive oil as an important source of monounsaturated fat, and allows low to moderate wine consumption. It generally includes low to moderate amounts of fish, poultry, and dairy products, with little red meat. Although the Mediterranean diet is associated with several health benefits, it remains uncertain if a single component of the Mediterranean diet offers the protective benefit or if the benefit results from an aggregation of effects.

In a meta-analysis of randomized trials including the large PREDIMED trial [107], a Mediterranean diet reduced the risk of stroke compared with a low-fat diet (HR 0.60, 95% CI 0.45 to 0.80) but did not reduce the incidence of cardiovascular or overall mortality [108]. By contrast, in observational studies, a Mediterranean diet was associated with lower overall mortality and cardiovascular mortality [109-112].

Additionally, in observational studies, a Mediterranean diet was also associated with a decreased incidence of Parkinson disease, Alzheimer disease, and cancers, including colorectal, prostate, aerodigestive, oropharyngeal, and breast cancers [109,110,113-115]. (See "Factors that modify breast cancer risk in women".)

The effects of the Mediterranean diet on type 2 diabetes mellitus are discussed separately. (See "Nutritional considerations in type 2 diabetes mellitus", section on 'Macronutrient composition'.)

Organic diet — There is significant interest in the potential health benefits of eating an organic diet. Although there are regulatory definitions for what qualifies as organic produce and organic egg, meat, and dairy products [116], there is a lack of established methodology in assessing what actually qualifies as an organic diet. In addition, complicating the research on the impact of organic food on health is the difficulty of taking fully into account the potential confounders linked with organic food consumption (eg, other elements of a healthy lifestyle) [117].

Despite great interest in the area, high-quality data are still lacking on the links between the consumption of organic food and improved health. While eating a diet high in organic foods can lessen exposure to synthetic pesticides, it is unclear if this actually translates to improved health outcomes [117,118]. Growing evidence does, however, point to a possible link between high organic food intake and a lower risk of cancer, particularly non-Hodgkin lymphoma [119,120]. Further evidence from well-designed studies is needed to confirm this association.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Vitamin deficiencies" and "Society guideline links: Healthy diet in adults".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Diet and health (The Basics)" and "Patient education: Vegetarian diet (The Basics)" and "Patient education: Vitamin supplements (The Basics)" and "Patient education: Can foods or supplements lower cholesterol? (The Basics)")

●Beyond the Basics topics (see "Patient education: Diet and health (Beyond the Basics)" and "Patient education: High-fiber diet (Beyond the Basics)")

●The Healthy Eating Plate offers guidance to patients to make healthy eating choices.

SUMMARY AND RECOMMENDATIONS

●Maintaining caloric balance over time is important to maintaining healthy weight. Balancing caloric intake requires that many individuals decrease their typical calorie consumption while also engaging in physical activity. Calculating total energy expenditure for recommended daily caloric intake is based on age, sex, weight, and activity level (table 1). (See 'Caloric balance' above and "The benefits and risks of aerobic exercise".)

●Caloric intake should be proportioned among the three macronutrients: carbohydrates, proteins, and fats. Macronutrients are the chemical compounds consumed in the largest quantities and provide bulk energy. (See 'Macronutrients' above and "Dietary fat".)

●Micronutrients are nutrients required in small amounts and include several minerals and vitamins. (See 'Micronutrients' above and "Vitamin supplementation in disease prevention" and "Salt intake, salt restriction, and primary (essential) hypertension".)

•The recommended dietary sodium intake for the general population is less than 100 mEq/day (2.3 g of sodium or 6 g of sodium chloride). Low sodium intake is associated with decreased risk of cardiovascular events, including death.

•Most individuals who consume a balanced diet do not need to take vitamin supplements.

●The main food groups generally consist of fruits/vegetables, grains, dairy products, and protein-rich foods.

•Individuals should be counseled to consume five or more servings of fruits and/or vegetables daily. Fruits and vegetables are a rich source of fiber, and fruit/vegetable consumption is inversely associated with risk of coronary heart disease (CHD), stroke, and mortality. (See 'Fruits and vegetables' above.)

•Individuals should be advised to replace refined grains (eg, white bread, white rice, refined and sweetened cereals) with whole grains (eg, whole-wheat bread, brown rice, whole-grain cereals or oatmeal), which have a higher content of fiber and other nutrients (table 4). Refined grains are associated with long-term weight gain. Whole grains are associated with a lower risk of heart disease, diabetes, colorectal cancer, and premature mortality. (See 'Grains' above.)

•Trans fatty acid consumption should be kept as low as possible by limiting foods such as partially hydrogenated oils, which are found in stick margarine and in many store-bought, processed, and fast foods. (See "Dietary fat", section on 'Trans fatty acids'.)

•We continue to advise people to moderate their intake of red and processed meats and to eat a variety of healthy protein-rich foods, including seafood, lean meat (such as poultry), eggs, beans, peas, soy products, and unsalted nuts and seeds. Consumption of red and processed meats is associated with a moderate increase in mortality compared with consumption of white meat. (See 'Protein' above and 'Protein-rich foods' above.)

●The consumption of soft drinks and other sweetened beverages (eg, fruit drinks, sports drinks, and energy drinks) is a major source of added refined sugar and calories in the diet and should be discouraged. (See 'Sweetened beverages' above.)

●Low-fat diet, vegetarian diets, Dietary Approaches to Stop Hypertension (DASH) diet, and the Mediterranean diet are among the most commonly used diets to maintain good health, where weight loss is not necessarily the primary goal. These diets are associated with health benefits. However, it is not known which type of diet is optimal for the general population. The decision to choose one of these diets is generally based on individual risk factors, personal preference, and the ability to adhere to a given diet. (See 'Types of diet' above and "Obesity in adults: Dietary therapy".)