House Call: Could Intermittent Fasting Be the Key to Your Weight Loss?

Plate half filled with food

Photo: Westend61/Getty Images

…But not famine. Here, Dr. Zachary Levine chews on the benefits of fasting

Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It’s currently very popular in the health and fitness community. It has been shown to be an effective form of weight loss (like calorie restriction diets), with some potential added health benefits. In fact, studies on rats with intermittent fasting show that they lose weight and their blood pressure, cholesterol and blood sugars improve.

How does intermittent fasting work? The food we eat is broken down into molecules that enter our bloodstream. Carbohydrates, particularly refined grains (especially white flours and rice) are broken down into sugar, which our cells use for energy. Sugar can only enter our cells with insulin, a hormone made in the pancreas. Insulin brings sugar into the fat cells and keeps it there.

If our cells don’t use the sugar, we store the extra as fat. Between meals, as long as we don’t snack, our insulin levels will go down, and our fat cells can then release their stored sugar, to be used as energy. We lose weight if we let our insulin levels go down. Intermittent fasting allows insulin levels to go down far enough and for long enough that we burn off our fat.

There is evidence that eating earlier in the day and extending the overnight fast significantly benefits metabolism (increased insulin sensitivity and lower blood pressure) independent of any weight loss. In fact, nighttime eating is
associated with a higher risk of obesity and diabetes.

There are several methods of intermittent fasting. One is the 16/8 method, wherein you eat for eight of 24 hours per day, such as from 7 a.m. to 3 p.m., or noon to 8 p.m. Another method is fasting for 24 hours once or twice a week. Many people find this difficult. A third method is consuming only 500 to 600 calories twice per week.

Most people find the 16/8 method most sustainable, and there is evidence that doing it earlier in the day (i.e., 7 a.m. to 3 p.m.) is most beneficial.

By reducing calorie intake, all of these methods should cause weight loss as long as you don’t compensate by eating much more during the eating periods.

In addition to weight loss, proponents of the diet state that it has other positive effects: increased Human Growth Hormone (HGH), which is good for lean muscle mass; lower insulin levels, allowing the body to use stored fat; better cellular repair; and there is early evidence that it can help extend life expectancy (like calorie restriction) and protect against dementia.

Intermittent fasting is not for everyone. In lieu of that, the best advice is to avoid sugars and refined carbohydrates, give your body time to burn fat between meals and avoid snacking or late night eating. More specifically, the following people should talk to their doctor before considering IF: those with diabetes or glucose regulation problems, those who take medications, those with a history of eating disorder, women who are breastfeeding, pregnant or trying to conceive and those with chronic medical conditions.

A version of this article appeared in the July/August 2019 issue with the headline, “Feast or Fast,” p. 24.