A healthy diet is a diet that helps to maintain or improve overall health. A healthy diet provides the body with essential nutrition: fluid, macronutrients, micronutrients, and adequate calories.[1][2]

For people who are healthy, a healthy diet is not complicated and contains mostly fruits, vegetables, and whole grains, and includes little to no processed food and sweetened beverages. The requirements for a healthy diet can be met from a variety of plant-based and animal-based foods, although a non-animal source of vitamin B12 is needed for those following a vegan diet.[3] Various nutrition guides are published by medical and governmental institutions to educate individuals on what they should be eating to be healthy. Nutrition facts labels are also mandatory in some countries to allow consumers to choose between foods based on the components relevant to health.[4]

A healthy lifestyle includes getting exercise every day along with eating a healthy diet. A healthy lifestyle may lower disease risks, such as obesity, heart disease, type 2 diabetes, hypercholesterolemia, hypertension and cancer.[1][5]

There are specialized healthy diets, called medical nutrition therapy, for people with various diseases or conditions. There are also prescientific ideas about such specialized diets, as in dietary therapy in traditional Chinese medicine.

The World Health Organization (WHO) makes the following five recommendations with respect to both populations and individuals:[6]

The WHO has stated that insufficient vegetables and fruit is the cause of 2.8% of deaths worldwide.[8]

Other WHO recommendations include:

The Dietary Guidelines for Americans by the United States Department of Agriculture (USDA) recommends three healthy patterns of diet, summarized in the table below, for a 2000 kcal diet.[9]

It emphasizes both health and environmental sustainability and a flexible approach. The committee that drafted it wrote: "The major findings regarding sustainable diets were that a diet higher in plant-based foods, such as vegetables, fruits, whole grains, legumes, nuts, and seeds, and lower in calories and animal-based foods is more health promoting and is associated with less environmental impact than is the current U.S. diet. This pattern of eating can be achieved through a variety of dietary patterns, including the Healthy U.S.-style Pattern, the Healthy Vegetarian Pattern" and the "Healthy Mediterranean-style Pattern".[10] Food group amounts are per day, unless noted per week.

The American Heart Association, World Cancer Research Fund, and American Institute for Cancer Research recommend a diet that consists mostly of unprocessed plant foods, with emphasis on a wide range of whole grains, legumes, and non-starchy vegetables and fruits. This healthy diet includes a wide range of non-starchy vegetables and fruits which provide different colors including red, green, yellow, white, purple, and orange. The recommendations note that tomato cooked with oil, allium vegetables like garlic, and cruciferous vegetables like cauliflower, provide some protection against cancer. This healthy diet is low in energy density, which may protect against weight gain and associated diseases. Finally, limiting consumption of sugary drinks, limiting energy rich foods, including fast foods and red meat, and avoiding processed meats improves health and longevity. Overall, researchers and medical policy conclude that this healthy diet can reduce the risk of chronic disease and cancer.[11][12]

It is recommended that children consume less than 25 grams of added sugar (100 calories) per day.[13] Other recommendations include no extra sugars in those under 2 years old and less than one soft drink per week.[13] As of 2017, decreasing total fat is no longer recommended, but instead, the recommendation to lower risk of cardiovascular disease is to increase consumption of monounsaturated fats and polyunsaturated fats, while decreasing consumption of saturated fats.[14]

The Nutrition Source of Harvard School of Public Health makes the following 10 recommendations for a healthy diet:[15]

Other than nutrition, the guide recommends frequent physical exercise and maintaining a healthy body weight.[15]

David L. Katz, who reviewed the most prevalent popular diets in 2014, noted:

The weight of evidence strongly supports a theme of healthful eating while allowing for variations on that theme. A diet of minimally processed foods close to nature, predominantly plants, is decisively associated with health promotion and disease prevention and is consistent with the salient components of seemingly distinct dietary approaches.Efforts to improve public health through diet are forestalled not for want of knowledge about the optimal feeding of Homo sapiens but for distractions associated with exaggerated claims, and our failure to convert what we reliably know into what we routinely do. Knowledge in this case is not, as of yet, power; would that it were so.[21]

Marion Nestle expresses the mainstream view among scientists who study nutrition:[22]:10

The basic principles of good diets are so simple that I can summarize them in just ten words: eat less, move more, eat lots of fruits and vegetables. For additional clarification, a five-word modifier helps: go easy on junk foods. Follow these precepts and you will go a long way toward preventing the major diseases of our overfed societycoronary heart disease, certain cancers, diabetes, stroke, osteoporosis, and a host of others.... These precepts constitute the bottom line of what seem to be the far more complicated dietary recommendations of many health organizations and national and international governmentsthe forty-one key recommendations of the 2005 Dietary Guidelines, for example. ... Although you may feel as though advice about nutrition is constantly changing, the basic ideas behind my four precepts have not changed in half a century. And they leave plenty of room for enjoying the pleasures of food.[23]:22

In addition to dietary recommendations for the general population, there are many specific diets that have primarily been developed to promote better health in specific population groups, such as people with high blood pressure (such as low sodium diets or the more specific DASH diet), or people who are overweight or obese (weight control diets). However, some of them may have more or less evidence for beneficial effects in normal people as well.

A low sodium diet is beneficial for people with high blood pressure. The Cochrane review published in 2008 concluded that a long term (more than 4 weeks) low sodium diet usefully lowers blood pressure, both in people with hypertension (high blood pressure) and in those with normal blood pressure.[24]

The DASH diet (Dietary Approaches to Stop Hypertension) is a diet promoted by the National Heart, Lung, and Blood Institute (part of the NIH, a United States government organization) to control hypertension. A major feature of the plan is limiting intake of sodium,[25] and the diet also generally encourages the consumption of nuts, whole grains, fish, poultry, fruits, and vegetables while lowering the consumption of red meats, sweets, and sugar. It is also "rich in potassium, magnesium, and calcium, as well as protein".

The Mediterranean diet, which includes limiting consumption of red meat and using olive oil in cooking, has also been shown to improve cardiovascular outcomes.[26]

Most people who are overweight or obese can use dieting in combination with physical exercise to lose weight.

Diets to promote weight loss are divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie.[27] A meta-analysis of six randomized controlled trials found no difference between the main diet types (low calorie, low carbohydrate, and low fat), with a 24 kilogram weight loss in all studies.[27] After two years, all of the diets in the studies that reduced calories resulted in equal weight loss regardless of whether changes in fat or carbohydrate consumption were emphasized.[28]

Gluten, a mixture of proteins found in wheat and related grains including barley, rye, oat, and all their species and hybrids (such as spelt, kamut, and triticale),[29] causes health problems for those with gluten-related disorders, including celiac disease, non-celiac gluten sensitivity, gluten ataxia, dermatitis herpetiformis, and wheat allergy.[30] In these people, the gluten-free diet is the only available treatment.[31][32][33]

There may be a relationship between lifestyle including food consumption and lowering the risk of cancer and other chronic diseases. A diet high in fruit and vegetables appears to decrease the risk of cardiovascular disease and death, but not cancer.[34]

Eating a healthy diet and getting enough exercise can maintain body weight within the normal range and prevent obesity in most people, and thus prevent the chronic diseases and poor outcomes associated with obesity.[35]

The Western pattern diet which is typically eaten by Americans and increasingly adopted by people in the developing world as they leave poverty is unhealthy: it is "rich in red meat, dairy products, processed and artificially sweetened foods, and salt, with minimal intake of fruits, vegetables, fish, legumes, and whole grains."[36]

An unhealthy diet is a major risk factor for a number of chronic diseases including: high blood pressure, high cholesterol, diabetes, abnormal blood lipids, overweight/obesity, cardiovascular diseases, and cancer.[37]

The WHO estimates that 2.7 million deaths each year are attributable to a diet low in fruit and vegetables.[37] Globally such diets are estimated to cause about 19% of gastrointestinal cancer, 31% of ischaemic heart disease, and 11% of strokes,[5] thus making it one of the leading preventable causes of death worldwide.[38]

Some publicised diets, often referred to as fad diets, make promises of weight loss or other health advantages such as longer life without backing by solid science; many fad diets are based on highly restrictive or unusual food choices.[23]:296[39] Celebrity endorsements (including celebrity doctors) are frequently associated with such diets, and the individuals who develop and promote these programs often profit handsomely.[22]:1112[40]

Consumers are generally aware of the elements of a healthy diet, but find nutrition labels and diet advice in popular media confusing.[41]

Fears of high cholesterol were frequently voiced up until the mid-1990s. However, more recent research hasshown that the distinction between high- and low-density lipoprotein ('good' and 'bad' cholesterol, respectively) must be addressed when speaking of the potential ill effects of cholesterol. Different types of dietary fat have different effects on blood levels of cholesterol. For example, polyunsaturated fats tend to decrease both types of cholesterol; monounsaturated fats tend to lower LDL and raise HDL; saturated fats tend to either raise HDL, or raise both HDL and LDL;[42][43] and trans fat tend to raise LDL and lower HDL.

Dietary cholesterol is only found in animal products such as meat, eggs, and dairy. The effect of dietary cholesterol on blood cholesterol levels is controversial. Some studies have found a link between cholesterol consumption and serum cholesterol levels.[44] Other studies have not found a link between eating cholesterol and blood levels of cholesterol.[45]

Vending machines in particular have come under fire as being avenues of entry into schools for junk food promoters. However, there is little in the way of regulation and it is difficult for most people to properly analyze the real merits of a company referring to itself as "healthy." Recently, the Committee of Advertising Practice in the United Kingdom launched a proposal to limit media advertising for food and soft drink products high in fat, salt or sugar.[46] The British Heart Foundation released its own government-funded advertisements, labeled "Food4Thought", which were targeted at children and adults to discourage unhealthy habits of consuming junk food.[47]

From a psychological and cultural perspective, a healthier diet may be difficult to achieve for people with poor eating habits.[48] This may be due to tastes acquired in childhood and preferences for sugary, salty and/or fatty foods.[49] In the UK, the chief medical officer of the government recommended in December 2018 that sugar and salt be taxed to discourage consumption.[50]

Animals that are kept by humans also benefit from a healthy diet, but the requirements of such diets may be very different from the ideal human diet.[51]

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