enough exercise can maintain body weight within the normal range and reduce the risk of obesity in most people. a 2021 scientific review of evidence on diets for lowering the risk of atherosclerosis found that: low consumption of salt and foods of animal origin, and increased intake of plant-based foods—whole grains, fruits, vegetables, legumes, and nuts—are linked with reduced atherosclerosis risk. the same applies for the replacement of butter and other animal/tropical fats with olive oil and other unsaturated-fat-rich oil. with regard to meat, new evidence differentiates processed and red meat—both associated with increased cvd risk—from poultry, showing a neutral relationship with cvd for moderate intakes. new data endorse the replacement of most high glycemic index (gi) foods with both whole grain and low gi cereal foods. scientific research is also investigating impacts of nutrition on health- and lifespans beyond any specific range of diseases. research suggests that increasing adherence to mediterranean diet patterns is associated with a reduction in total and cause-specific mortality, extending health- and lifespan. research is identifying the key beneficial components of the mediterranean diet. it shares various characteristics with the similarly beneficial okinawa diet. potential anti-aging mechanisms of various nutrients are not yet understood. shares of macronutrients and level of caloric intake may also be of significance, including in periods when no dietary restriction occurs – such as not having a fat-intake that is too low and not having a prolonged caloric surplus or caloric deficit that is too large. studies suggest dietary changes are a major cause of national relative rises in life-span. microbiome mechanistically, research suggests that the gut microbiome, which varies per person and changes throughout lifespan, is also involved in the beneficial effects, due to which various diet supplementations with prebiotics, various diverse (multi-strain) probiotics and synbiotics, and fecal microbiota transplantation are being investigated for life extension, mainly for prolonging healthspan, with many important questions being unresolved. optimal diet expected life years gained for 20-year-olds in u.s. who change from a typical western diet to an, according to an integrative study, "optimized diet" (changes indicated on the left in gram) approaches to develop optimal diets for health- and lifespan (or "longevity diets") include: modifying or further particularizing the mediterranean diet as the baseline via nutrition science. for instance, via: (additional) increase in plant-based (but protein-rich) foods alongside additional restriction of meat intake – meat reduction is (or can be) typically healthy, regular moderate consumption of green tea or (filtered) coffee while ensuring adequate calcium intake (additional) increase in omega-3-containing seafoods (see also: algal oil) adding various foods thought to be healthy (e.g. due to results about various mechanistic effects) to the regular dietary consumption patterns (see also: functional food) increasing the intake of high-spermidine foods – studies suggest spermidine could extend lifespan, with high amounts that are larger than common supplements being present in fungi (e.g. mushrooms) and green peas increasing resistant starch-intake – legumes, especially e.g. green peas contain large amounts of resistant starch, especially if pre-cooked as cooling the cooked peas in a refrigerator substantially increases the resistant starch content due to starch retrogradation. it is a prebiotic (see microbiome) and may promote healthy aging. keeping alcohol consumption of any type at a minimum – conventional mediterranean diets include alcohol consumption (i.e. of wine), which is under research due to data suggesting negative long-term brain impacts even at low/moderate consumption levels. anthocyanins which are present in red wine and suggested along with other flavanols to be a candidate for further longevity research are also present in comparable concentrations in bilberry and elderberry fully replacing refined grains – some guidelines of mediterranean diets do not clarify or include the principle of whole-grain consumption instead of refined grains. whole-grain are a significant source of spermidine and are associated with longevity. they are a main characteristic pillar of mediterranean diets according to multiple reviews. aiming for a sufficient level of food variety and diversity – which some guidelines of mediterranean diets do not clarify or include. one review suggests that food variety and diversity could be a factor of diet quality, and another review indicates that sufficient food variety may at least in some specific cases "increase intake of important nutrients and positively affect the gut microbiome structure and function". the required level of food variety may or may not be low and vary per person and diet. completely eliminating processed foods from the diet – some guidelines of mediterranean diets may not clarify this principle. diets associated with longevity are characterized by minimally processed foods. adjusting the diet for personal characteristics such as age as effects of e.g. macronutrient intake can vary per age (see below) inferring an optimal diet indiscriminately for all levels and forms of physical activities and age and other person-characteristics by integrating the available meta-analyses and data from mostly observational studies. this has been done for a tool and visualizations that show populations' relative general life extension potentials of (shifting diets towards) different food groups, suggesting i.a. that a 20-years old male in europe who switches to the "optimal diet" could gain a mean of ~13.7 years of life and a 60-years old female in the u.s. switching to the "optimal diet" could gain a mean of ~8.0 years of life. it found the largest gains would be made by eating more legumes, whole grains, and nuts, and less red meat and processed meat. the optimal diet contains no consumption of sugar-sweetened beverages (moving from "typical western diet" of 500 g/day to 0 g/day). the study notes of uncertainty in "the effect of eggs, white meat, and oils, individual variation in protective and risk factors, uncertainties for future development of medical treatments; and changes in lifestyle". moreover, not only do the components of diets matter but the total caloric content and eating patterns may also impact health – dietary restriction such as caloric restriction is considered to be potentially healthy to include in eating patterns in various ways in terms of health- and lifespan. unhealthy diets 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. the world health organization has estimated that 2.7 million deaths each year are attributable to a diet low in fruit and vegetables during the 21st century. globally, such diets are 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, and the 4th leading risk factor for any disease. as an example, the western pattern diet 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," contrasted by the mediterranean diet which is associated with less morbidity and mortality. fad diet further information: fad diet some publicized diets, often referred to as fad diets, make exaggerated claims of fast weight loss or other health advantages, such as longer life or detoxification without clinical evidence; many fad diets are based on highly restrictive or unusual food choices. celebrity endorsements (including celebrity doctors) are frequently associated with such diets, and the individuals who develop and promote these programs often profit considerably.: 11–12 public health consumers are generally aware of the elements of a healthy diet, but find nutrition labels and diet advice in popular media confusing. fears of high cholesterol were frequently voiced up until the mid-1990s. later research shows that the distinction between high- and low-density lipoprotein is vital when considering 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 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. other studies have not found a link between eating cholesterol and blood levels of cholesterol. vending machines in particular have come under fire as being avenues of entry into schools for junk food promoters, but 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." 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. 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. 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 fatty foods. in 2018, the uk chief medical officer recommended that sugar and salt be taxed to discourage consumption. the uk government 2020 obesity strategy encourages healthier choices by restricting point-of-sale promotions of less-healthy foods and drinks. other animals 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.