Calorie Restriction and Fasting Diet

January 10, 2021

4 min read

Fasting diets have been gaining a lot of attention in the media. The reasons people give for trying these diets include weight loss or maintenance, general health improvement, increased vitality, and increased lifespan. The health impacts of fasting diets are still not fully understood, and research in this area is active.

Types of Fasting Diets

Caloric restriction aims to maintain consumption of essential nutrients, so the person does not become malnourished. Fasting is defined as a period of avoiding calorie intake. While standard diets focus only on consistent overall daily caloric restriction, a fasting diet achieves this by limiting the times that a person eats or drinks. Periods of fasting usually decrease the number of calories consumed each day, but that is not always the case, depending on the foods chosen during non-fasting hours. Fasting diets are often called “intermittent fasting,” because the person will alternate periods of fasting and eating on a set schedule. The National Institute on Agingnotes 4 common fasting schedules:

Time restricted: Meals may only be consumed withing a set time period each day. Often these periods are the 6 to 8 hours in the middle of the day. During the other hours, nothing is consumed, except water or other calorie-free beverages. This method of fasting is probably the most popular today.
Period fasting: Eating patterns are mostly unchanged, except for set periods of longer-term fasting. For example, a person may fast for 5 days in row each month. On all other days, they eat and drink whenever they want.
Alternate-day fasting: A person alternates between a day of eating no or minimal calories and day of eating unrestricted calories. This pattern is repeated indefinitely.
5:2 pattern: For 5 days each week, the person eats whenever they want. Then, they fast or restrict calories for 2 days.

Potential Health Benefits of Fasting Diets and Caloric Restriction

Modern day people suffer from a number of diseases related to over nutrition or poor diet. Many people suffer from metabolic syndrome, which is characterized by obesity, insulin resistance (precursor to diabetes), high lipids, and high blood pressure. Having multiple symptoms of metabolic syndrome increases the risk of stroke, heart attack, and diabetes. The first line of defense is to make healthy lifestyle changes, including improved diet and exercise. Caloric restriction is often recommended, and numerous studies in animals have shown that it can decrease the rate of aging and increase lifespan. Fasting diets are often recommended because they are easy for people to follow. Potential positive impacts of caloric restriction include the following:

Decreased biomarkers of aging, such as insulin and age-related hormones
Decreased risk factors and accelerators of heart disease, including lipids, cholesterol, and blood pressure
Normalized sensitivity to glucose, thereby decreasing the risk of diabetes
Weight loss
Lowered metabolic rate, which may decrease the amount of oxidative damage to vital tissues and DNA. This could reduce the number of cancers or signs of biological aging.

Together, these potential affects can add up to reduce the amount of age-related diseases and improve overall health. In some cases, people have successfully reverse diabetes, obesity, and heart disease through dietary changes. They may slow the rate of aging and increase lifespan. However, most studies have been done in laboratory animals, and studies in humans are limited. Available work in humans has shown varied results, although some have been promising in showing that caloric restriction decreases the rate of aging and improves overall health.

Ketones

Increasing compounds in the blood called ketones is often cited as a benefit of intermittent fasting. When the body is not receiving calories in the form of food or drink, it first must use up stores of glucoses and glycogen. Then, it will turn to breaking down stored fat for energy. This breakdown of fat releases energy in the form of ketones.

Ketones are used by the brain as an energy source. Some scientists have hypothesized that ketones may be a more efficient energy source than glucose in the brain, which could protect against dementia and other central nervous system disorders. In addition, cancer cells may not be able to efficiently use ketones, potentially protecting the body from cancer progression. Other studies suggest ketones may protect against inflammation (e.g., decreased arthritis) and decrease the amount of insulin in the blood (i.e., decreased diabetes). These effects may help explain some benefits of caloric restriction. However, doctors know that too many ketones in the blood can be harmful, so it could be dangerous to alter the balance of ketones in the body too much.

Effects of Caloric Restriction and Fasting Diets

Caloric restriction is not easy for many people. Like many types of diets, it can be difficult to maintain because the side effects can be unbearable over the long term. Common side effects include:

Depressed mood
Irritability
Decreased energy
Development of eating disorder symptoms (e.g., binge eating, anorexia, or bulimia)
Reduced sexual interest
Decreased ability to maintain body temperature in cold environments

The experience of fasting diets can change over time. Some people are not able to maintain them even or short periods of time. Other people who initially struggle with these diets find that they become easier over time.

Is a Fasting Diet the Best Choice for You?

According to FoodIntake.org, despite the popularity of intermittent fasting, there is not yet enough long-term research to demonstrate the health benefits. The metabolism of the human body is incredibly complex. Researchers are still trying to understand how dietary changes affect metabolism, and they are further still from understanding the long-term effects on the human body. Since specific healthy foods and nutrients are not recommending by intermittent fasting diets, traditional diets that encourage caloric restriction with nutrient dense foods are more likely to be beneficial. Traditional diets include Mediterranean, Nordic, MIND and DASH. These are also easier for most people to follow long term.