Diet Therapy

Intermittent fasting has various forms, including restricting eating to certain times of the day (usually less than 10 hours, often called time-restricted feeding) or not eating for a day or longer (eg, alternate-day fasting). Intermittent fasting causes a metabolic switch from using glucose from the liver to ketones stored in fat (1). It has been shown to have favorable metabolic effects (eg, increased insulin sensitivity and autophagy, possibly increased lifespan) in animal studies (2). Health benefits in humans include reduced body weight and waist circumference compared to no dietary intervention, although long-term efficacy is uncertain (3). Whether intermittent fasting is more effective than general caloric restriction is also a question (4). One concern with weight loss by fasting is concurrent loss of lean body mass while losing fat mass (5); although loss of fat mass may contribute to metabolic benefits, this may be offset by the detrimental health effects of losing muscle mass  (6).

This diet consists mainly of vegetables, whole grains, fruits, and cereals. While claims have been made that this diet can prevent and treat cancer and other chronic disorders, there is no high-quality evidence to support the efficacy of a macrobiotic diet for the prevention or treatment of cancer or its recurrence (1). The macrobiotic diet has also been investigated in patients with metabolic syndrome, prediabetes, and diabetes without conclusive evidence of efficacy (2).

Risks of following this diet, other than lack of efficacy in disease prevention or therapy, are few (3).

This very low fat vegetarian diet aims to help reverse arterial blockages that cause coronary artery disease and may help prevent or slow the progression of prostate and other cancers. It focuses on plant-based foods and avoidance of fat, refined carbohydrates, and animal protein. As a component of an intensive lifestyle program for participants with symptomatic coronary artery disease, the Ornish diet is effective (1). However, it is not clear whether the specific food restrictions of the diet offer unique benefits. Similar outcomes may be achieved with other diets that reduce less healthful fats and refined carbohydrates without restricting healthier fats (eg, olive oil).

This diet consists of types of food allegedly consumed during the Paleolithic era, when food was hunted or gathered (ie, animals and wild plants). Thus, the diet includes

• Increased protein intake

• Decreased carbohydrate intake (with intake mainly of nonstarchy fresh fruits and vegetables)

• A moderate to higher fat intake (with intake mainly of monounsaturated and polyunsaturated fats)

Foods thought not to be available during the Paleolithic era (eg, dairy products, grains, legumes, processed oils, refined sugar, salt, coffee) are avoided. Proponents claim that human metabolism has not adapted to handle many of these foods.

The Paleo diet is thought to treat or reduce the risk of coronary artery disease, metabolic syndrome, type 2 diabetes, and many chronic degenerative disorders (1, 2). The Paleo diet also potentially promotes weight loss, improves athletic performance, enhances sleep, and improves mental function. However, there is limited evidence concerning the efficacy of this diet.

Risks include inadequate nutrition (due to decreased intake of whole grains and dairy).

Knowledge of what was eaten in the Paleolithic era is limited; however, some evidence suggests that the diet of the Paleolithic era was not as limited as the modern Paleo diet.

The keto diet, similar to the Paleo diet, contains very high fat-containing foods and very low amounts of carbohydrates. The diet aims to induce ketosis, a state in which fat is burned as the source of energy, resulting in weight loss. The keto diet has been shown to suppress hunger, resulting in decreased weight, waist circumference, triglycerides, hemoglobin A1C, and blood glucose (1–3).

Typical foods in the keto diet include avocados, oils, nuts, fatty fish, eggs, beef, chicken, vegetables, cheese, butter, and cream. The restricted diet is not always palatable, and adherence is a challenge.

Risks include gastrointestinal symptoms such as constipation, nausea, vomiting, and diarrhea. Individuals may experience the so called "keto flu," which is characterized by headache, fatigue, irritability, difficulty sleeping, and nausea. Other risks include dyslipidemia with increased LDL levels, nephrolithiasis, hepatic steatosis, hypercalciuria, hypoproteinemia, and anemia (4–6).