Major function of Healthy Diet

A healthy diet is one that helps maintain or improve general health. It is thought to be important for lowering health risks, such as obesity, heart disease, diabetes, hypertension and cancer. A healthy diet involves consuming primarily fruits, vegetables, and whole grains to satisfy caloric requirements, provide the body with essential nutrients, phytochemicals, and fibre, and provide adequate water intake. A healthy diet supports energy needs and provides for human nutrition without exposure to toxicity or excessive weight gain from consuming excessive amounts.

The World Health Organization (WHO) makes the following 5 recommendations with respect to both populations and individuals:

• Eat roughly the same amount of calories that your body is using. A healthy weight is a balance between energy consumed and energy that is 'burnt off'.
• Increase consumption of plant foods, particularly fruits, vegetables, legumes, whole grains and nuts.
• Limit intake of fats, namely saturated fats and trans fats and replace with healthier unsaturated fats.
• Limit the intake of granulated sugar. A 2003 report recommends less than 10% simple sugars.
• Limit salt / sodium consumption from all sources and ensure that salt is iodized.

Other recommendations include:

• Essential micronutrients such as vitamins and certain minerals.
• Avoiding directly poisonous (e.g. heavy metals) and carcinogenic (e.g. benzene) substances.
• Avoiding foods contaminated by human pathogens (e.g. E. coli, tapeworm eggs).

10 recommendations for a healthy diet:

• Choose good carbohydrates: whole grains (the less processed the better), vegetables, fruits and beans. Avoid white bread, white rice, and the like as well as pastries, sugared sodas, and other highly-processed food.
• Pay attention to the protein package: good choices include fish, poultry, nuts, and beans. Try to avoid red meat.
• Choose foods containing healthy fats. Plant oils, nuts, and fish are the best choices. Limit consumption of saturated fats, and avoid foods with trans fat.
• Choose a fiber-filled diet which includes whole grains, vegetables, and fruits.
• Eat more vegetables and fruits—the more colorful and varied, the better.
• Calcium is important, but milk is not its best source. Good sources of calcium are collards, bok choy, fortified soy milk, baked beans, and supplements which contain calcium and vitamin D.
• Water is the best source of liquid. Avoid sugary drinks, and limit intake of juices and milk. Coffee, tea, artificially-sweetened drinks, 100-percent fruit juices, low-fat milk and alcohol can fit into a healthy diet but are best consumed in moderation. Sports drinks are recommended only for people who exercise more than an hour at a stretch to replace substances lost in sweat.
• Limit salt intake. Choose more fresh foods, instead of processed ones.
• Moderate alcohol drinking has health benefits, but is not recommended for everyone.
• Daily multivitamin and extra vitamin D intake has potential health benefits.

Other than nutrition, the guide recommends frequent physical activity (exercise) and maintaining a healthy body weight.

For specific conditions

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 (as in low sodium diets or the more specific DASH diet), or people who are overweight or obese (in weight control diets). However, some of them may have more or less evidence for beneficial effects in normal people as well.
 

Hypertension

A low sodium diet is beneficial for people with high blood pressure. A Cochrane review published in 2008 concluded that a long term (more than 4 weeks) low sodium diet in Caucasians has a useful effect to reduce blood pressure, both in people with hypertension and in people with normal blood pressure.
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, and it 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". Evidence shows that the Mediterranean diet improves cardiovascular outcomes.

Obesity

Weight control diets aim to maintain a controlled weight. In most cases dieting is used in combination with physical exercise to lose weight in those who are overweight or obese.
Diets to promote weight loss are generally divided into four categories: low-fat, low-carbohydrate, low-calorie, and very low calorie. 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 2–4 kilogram weight loss in all studies. At two years, all calorie-reduced diet types cause equal weight loss irrespective of the macronutrients emphasized.


 

Diet and possible reduced disease risk

Further information: Diet and cancer

There may be a relationship between lifestyle including food consumption and potentially lowering the risk of cancer or other chronic diseases. A healthy diet may consist mostly of whole plant foods, with limited consumption of energy-dense foods, red meat, alcoholic drinks and salt while reducing consumption of sugary drinks, and processed meat. A healthy diet may contain non-starchy vegetables and fruits, including those with red, green, yellow, white, purple or orange pigments. Tomato cooked with oil, allium vegetables like garlic, and cruciferous vegetables like cauliflower "probably" contain compounds which are under research for their possible anti-cancer activity.
 
A healthy diet is low in energy density, lowering caloric content, thereby possibly inhibiting weight gain and lowering risk against chronic diseases. Chronic Western diseases are associated with pathologically increased IGF-1 levels. Findings in molecular biology and epidemiologic data suggest that milk consumption is a promoter of chronic diseases of Western nations, including atherosclerosis, carcinogenesis and neurodegenerative diseases.

Unhealthy diets

An unhealthy diet is a major risk factor for a number of chronic diseases including: high blood pressure, diabetes, abnormal blood lipids, overweight/obesity, cardiovascular diseases, and cancer.
The WHO estimates that 2.7 million deaths are attributable to a diet low in fruit and vegetable every year. Globally it is estimated to cause about 19% of gastrointestinal cancer, 31% of ischaemic heart disease, and 11% of strokes, thus making it one of the leading preventable causes of death worldwide.

Fad diets

Fad diet usually refers to idiosyncratic diets and eating patterns. They are diets that claim to promote weight loss or treat obesity by various mechanisms, provide little to no scientific reasoning behind their purported health benefits, and have little or no proof to support them.

Public health

Fears of high cholesterol were frequently voiced up until the mid-1990s. However, more recent research has shown 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; and trans fat tend to raise LDL and lower HDL. Dietary cholesterol itself is only found in animal products such as meat, eggs, and dairy, but studies have shown that even large amounts of dietary cholesterol only have negligible effects on blood cholesterol.
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 United Kingdom removed the rights for McDonald's to advertise its products, as the majority of the foods that were seen have low nutrient values and high fat counts were aimed at children under the guise of the "Happy Meal". The British Heart Foundation released its own government-funded advertisements, labeled "Food4Thought", which were targeted at children and adults displaying the gory nature of how fast food is generally constituted.

Cultural and psychological factors

From a psychological and cultural perspective, a healthier diet may be difficult to achieve for people with poor eating habits. This may be due to tastes acquired in childhood and preferences for sugary, salty and/or fatty foods.