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Calorie Restriction and Fasting Are Not the Same

Many people assume that the terms “calorie restriction” and “fasting” are interchangeable.

According to the National Institute on Aging (NIA), a division of the National Institutes of Health, calorie restriction is synonymous with reducing average daily caloric intake below what is typical or habitual – without malnutrition or deprivation of essential nutrients. In fasting, the individual does not eat at all or severely limits intake during certain times of the day, week, or month.

The NIA says they’re multiple intermittent-type fasting diets that fit the criteria. Time-restricted feedings involve meals being consumed within a window (hours) of a twenty-four-hour day – like between 8 am and 8 pm.

Alternate-day-fasting requires unrestricted food intake on an alternate day basis, while fasting on the days in between.

Five-two eating provides for unrestricted eating on 5 days – as in the work week – with fasting for 2 days – such as on the weekend.

Periodic fasting has a restricted calorie intake consumed for a block of consecutive days – 3 to 5 days – once a month, followed by unrestricted food intake on all other days.

The NIA says more animal research has been performed under calorie restriction conditions versus fasting.

In these studies, when rodents and other animals were given 10 percent to 40 percent fewer calories than usual, but provided with all necessary nutrients, many showed extension of lifespan and reduced rates of several diseases, especially cancers,” notes the NIA.

However, research demonstrated that, “some studies did not show this benefit, and in some mouse strains, calorie restriction shortened lifespan rather than extending it.”

As for human studies on calorie restriction, there may be benefits, but long-term outcomes on longevity are pending. Some people have voluntarily practiced extreme degrees of calorie restriction over many years in the belief that it will extend lifespan or preserve health, states the NIA.

The NIA qualifies this research by pointing out that, “studies on these individuals have found markedly low levels of risk factors for cardiovascular disease and diabetes. The studies have also found many other physiologic effects whose long-term benefits and risks are uncertain, as well as, reductions in sexual interest and the ability to maintain body temperature in cold environments.”

For fasting, research has centered primarily on obese individuals – with few clinical trials. The NIA reflects on one observational study that compared people who routinely fasted (as part of a religious practice or for another reason) to those who did not fast. “It found that those who routinely fasted were less likely to have clogged arteries or coronary artery disease. However, the study did not control for other factors that could have affected the results, such as the kind of diet, quality of food consumed, or use of nutritional supplements.”

In the CALERIE study (Long-term Effects of Reducing Intake of Energy), 218 young and middle-aged, normal-weight or moderately overweight adults were recruited to be randomly divided into two groups. Experimental participants were asked to follow a calorie-restriction diet for 2 years – consuming 25 percent fewer calories per day than their pre-study normal intake. The control group followed their usual diet.

In reality, the experimental group reduced their daily caloric intake by 12 percent – maintaining, on average, a 10 percent loss in body weight over 2 years. Two years after the intervention ended, it was determined that participants had sustained much of this weight loss.

The NIA cautions that, “it’s important to note that calorie-restriction regimens are not starvation diets. The weight loss achieved with calorie restriction in the CALERIE trial resulted in body weights within the normal or overweight range.”

After decades of animal research, it appears that scientists don’t know why calorie restriction may extend lifespan and delay age-related diseases in animals. It might be that ketones – a product of fasting – may inhibit certain forms of cancer or inflammatory diseases, such as arthritis. Yet, too many ketones in the blood is not advisable.

Make sure to consult with your physician before experimenting.