Repercussions of the obesity epidemic are already being felt. Obesity increases a person's risk for metabolic syndrome, which in turn increases the risk of type 2 diabetes and cardiovascular disease. Obesity also directly raises the risk of developing diabetes by 10 to 20 times. Patients with poorly managed or uncontrolled type 2 diabetes are at an increased risk for a number of significant health complications, including heart disease, nerve damage, eye problems, and kidney disease [6].

Similarly, obesity is associated with hypertension. Evidence suggests that every 10 kg increase in body weight is associated with a 3 mm Hg increase in systolic and 2.3 mm Hg increase in diastolic blood pressure. Obesity is also associated with dyslipidemia and elevated levels of fibrinogen and C-reactive protein. All of these factors increase the risk of cardiovascular disease, including coronary heart disease, myocardial infarction, and heart failure, as well as stroke and chronic kidney failure [7].

Obesity also increases a person's risk for some less obvious, but equally significant, health complications. Increased weight burden on the body can worsen osteoarthritis and exacerbate respiratory problems, such as obstructive sleep apnea, asthma, and obesity hypoventilation syndrome. It can also damage the gallbladder, due to an increased tendency to develop gallstones, and the liver, through the development of non-alcoholic steatohepatitis (NASH), also known as metabolic-associated steatohepatitis (MASH). Finally, obesity also increases the risk for various forms of cancer [6].

Interestingly, younger generations may be driving some of these changes. Adults 18 to 24 years of age report pursuing healthier eating strategies for the purpose of improving mental health, the only age group to include this in the top three reasons for dieting. Additionally, more than 70% of adults 40 years and younger report considering the environment when choosing foods, making them more likely to choose products labeled as "carbon neutral" or "plant-based" [10].

Dieting has become so common in the United States that it has been referred to as a national pastime. Each year, approximately 50% of adults younger than 50 years of age report following a diet, with the majority of people pursuing that diet in an effort to either lose weight or improve overall health.

Since 2020, the nation's perceptions of obesity and diet have begun to change. Surveys suggest that many adults are interested in focusing on healthier behaviors in place of specific weight-loss goals and are following a diet or dietary pattern for this purpose. Many adults report dieting for other health-related reasons as well—37% for increased energy, 29% for digestive health, 28% for cardiovascular health, and 26% for better sleep [10].

Interestingly, younger generations may be driving some of these changes. Adults 18 to 24 years of age report pursuing healthier eating strategies for the purpose of improving mental health, the only age group to include this in the top three reasons for dieting. Additionally, more than 70% of adults 40 years and younger report considering the environment when choosing foods, making them more likely to choose products labeled as "carbon neutral" or "plant-based" [10].

In fact, the shift to "plant-based" foods is dramatic, with almost one in three adults reporting that they ate more protein from whole-plant sources in 2022 than the previous year. Additionally, 23% of adults report consuming plant-based dairy alternatives, and 18% report consuming more soy-based milk or yogurt [10].

The document also provides general guidance on the typical calorie requirements for people of different biological sexes and ages [11]:

19 to 30 years of age:

31 to 59 years of age:

60 years of age and older:

According to the U.S. Dietary Guidelines, a relatively healthy distribution of calories from these macronutrient groups is [11]:

Certain fats, called polyunsaturated fats, are important components of cell membranes and contribute to reduced levels of inflammation in the body. These are essential fatty acids and are considered part of a healthy diet. Patients may recognize the types of fats that fall into this class: omega-3 and omega-6 fatty acids. These are found in fish, seeds, nuts, soy, eggs, and many other foods [12].

Fiber can be either water-soluble or water-insoluble. Water-soluble fibers, such as oats, beta-glucans, and barley, help to lower both blood glucose and cholesterol levels. Water-insoluble fibers, such as wheat bran and rice bran, help the body digest food and improve bowel health. Each of these fibers can help to slow the absorption of other carbohydrates by the body, resulting in lower blood glucose levels after eating [13].

Some of the most popular diets over the past few decades have focused on reducing carbohydrate intake, such as the Atkins diet, ketogenic diet, and South Beach diet. The premise of these diets is that carbohydrates increase insulin levels and induce metabolic changes that cause weight gain.

Not surprisingly, added sugars increase the glycemic index of any food. Whole foods that contain natural sugar, on the other hand, may have a lower glycemic index than some people would expect. For example, many fruits, including apples, bananas, strawberries, and peaches, have relatively low glycemic indices. This is due to the fiber content of these foods. Whole grains, which are primarily comprised of carbohydrates, also have a lower glycemic index due to fiber content. Processed grains, on the other hand, such as white bread, corn flakes, and instant porridge, have a high glycemic index [20].

The Atkins diet is a high-fat, low-carbohydrate diet that does not utilize the glycemic index [22]. This diet follows four distinct phases, starting with very restrictive limitations on carbohydrate consumption and slowly allowing for increased intake as weight loss progresses. The initial, highly restrictive phase limits carbohydrate consumption to 20 grams per day and is intended to cause rapid weight loss. After this phase, weight loss occurs more slowly and the quantity of carbohydrates consumed increases in increments. The final phase, or lifetime maintenance, is intended to achieve a diet with a carbohydrate equilibrium that results in maintaining the target weight [23].

The Atkins diet seems to cause more short-term weight loss than a traditional low-fat diet. But at the end of one year, weight loss is similar to conventional low-fat diets [21,24,25]. Some experts suggest that Atkins and similar diets could have a beneficial role for jumpstarting weight loss, before switching to a long-term, more sustainable maintenance diet. However, there does not seem to be a long-term benefit with the Atkins diet when compared with other calorie-restrictive diets.

Plant-based diets encompass a wide range of dietary strategies:

Plant-based diets, including vegetarian and vegan diets, are safe when used appropriately. The Academy of Nutrition and Dietetics states that a nutritionally adequate vegetarian diet is appropriate for adults and children. However, it is particularly important to ensure that all nutritional needs are met when following a vegetarian diet. Nutrients of concern may include omega-3 fatty acids, iron, zinc, calcium, vitamin D, and vitamin B12 [59]. In fact, one observational study has found that following a vegetarian diet or vegan diet is associated with lower bone mineral density at the femoral neck and lumbar spine when compared with diets that incorporate animal products [60].

The Mediterranean diet is a balanced and nutrient-dense diet that originally gained popularity as a preventive measure for cardiovascular disease. It has also gained popularity for reducing the risk of dementia, management of diabetes, and improving overall health. It is a moderate-fat diet that emphasizes consuming large amounts of fruits, vegetables, fish, and whole grains, using olive oil as a fat source, and eating low amounts of dairy, red meat, and refined grains. It also allows for the consumption of wine in low-to-moderate amounts, although some forms of the diet exclude this component [62]. This diet is generally considered to be safe as long as nutritional needs are met.

Some other forms of fasting have also gained popularity, albeit less so than intermittent fasting. One form, alternate-day fasting, involves fasting followed by "feasting" on alternate days. On fasting days, ≤25% of baseline energy is consumed during that 24-hour period. On feasting days, food is consumed as desired. This cycle is then repeated indefinitely. Another form, periodic fasting, involves very low-calorie intake for one to six days weekly, followed by consuming food as desired for the remainder of the week. The most common type of periodic fasting is the 5:2 diet, which includes two days each week with a very low caloric intake [71].

Clinicians should be aware that some diets that are advertised as anti-inflammatory do not actually produce anti-inflammatory scores on the DII. Rather, some diets are simply trying to capitalize on the popularity of the anti-inflammatory dietary pattern. If a patient is interested in following an anti-inflammatory diet, let them know that they may be better off following established diets that score well on the DII, such as the Mediterranean diet and the paleo diet.

If a patient is interested in eating organic foods, let them know that it is not yet clear if organic foods are better for overall health. Considering the higher price point for these items, some patients may benefit more from other lifestyle changes.

A small study showed that following the paleo diet for three to five weeks reduces weight by about 2.3 kg in healthy volunteers [86]. A more recent study in postmenopausal adults with overweight showed that, when compared with a low-fat diet, the paleo diet increased weight loss by about 4–5 kg at 6, 12, and 18 months, but not at 24 months [87].

Keep in mind that due to the strict restriction on the foods that can be consumed, the paleo diet can be difficult for many people to follow long-term. Also, there is some concern that the paleo diet does not provide adequate amounts of calcium or vitamin D [88]. People following the paleo diet long-term may require supplementation to prevent nutrient deficiencies.

The Zone diet consists of 40% carbohydrates, 30% protein, and 30% fat, uses a 40-30-30 rule. It advocates for limited intake of grains and starches. The yet-unproven theory behind the Zone diet is that a balance of carbohydrates, proteins, and fats maintains insulin levels "in the zone" and therefore minimizes fat storage and inflammation. The Zone diet is promoted to reduce the insulin-to-glucagon ratio. According to Zone diet proponents, this reduction affects metabolism of eicosanoids, which are produced from polyunsaturated fatty acids. This is intended to produce a metabolic state with decreased hunger, increased weight loss, increased energy, enhanced immunity, and a reduction in chronic disease risk [23].