Can intermittent fasting help with weight loss?

Intermittent fasting — the use of a strict eating schedule to help with weight loss — continues to grow in popularity. But can it really help?

"Recent research has found that intermittent fasting has a similar or even modest benefit over traditional calorie-restriction dieting for weight loss," says Dr. Frank Hu, a professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health. "But perhaps its main advantage is its simplicity, making it easier to follow compared with other weight-loss plans."

Timing your eating

Whereas other weight-loss diets emphasize what you should and should not eat, and how much, intermittent fasting focuses on when you can eat.

Intermittent fasting means you don't eat for a designated amount of time during the course of the day. There are many ways to do this, but one of the most popular approaches is called 16/8. Here, you do all your eating during an eight-hour period (for example, from 10 a.m. to 6 p.m.) and then don't eat at all over the following 16 hours (in this case, from 6 p.m. until 10 a.m. the next day). The pattern then repeats.

You can drink plain water, tea, or coffee during the fasting period, and you need to follow regular healthy eating habits during your eight-hour eating window.

Short-term studies suggest that people stick to intermittent fasting diets better than low-carb diets. "The 16/8 schedule is often easier to follow, since you sleep for about half of the fasting period," says Dr. Hu. "You just don't eat after dinner — no nighttime snacking — and either skip or postpone breakfast."

The state of ketosis

How might intermittent fasting help with weight loss? Not eating for such a long period can place the body in short-term ketosis, where the body burns fat for energy, according to Dr. Hu.

Ketosis is the metabolic process that kicks in when your body runs out of glucose (its preferred energy source) and begins burning stored fat. "Sixteen hours of not eating is sufficient for some people to start producing ketones or go into ketosis," says Dr. Hu.

Intermittent fasting has been linked with various health benefits, such as reducing cardiovascular disease risk factors, such as obesity, high blood sugar, high blood pressure, and high cholesterol. Research has also suggested it may be linked to a healthier gut microbiome, with possible improved digestion and protection against infections. Some people who follow intermittent fasting claim it helps increase energy levels, too.

Still, the existing evidence of intermediate fasting's benefits is limited, and any long-term benefits or drawbacks are unknown. "Most studies have not looked at large populations and only explored its effect over several weeks or up to one year," says Dr. Hu.

Go slow with fasting

Should you try intermittent fasting to help with weight loss? There doesn't appear to be much downside, and the approach may help you manage your eating habits, according to Dr. Hu. "For instance, it could help reduce your daily calories, especially if you're a late-night snacker."

Check with your doctor before trying intermittent fasting, especially if you have diabetes, take blood pressure medication, or tend to get dizzy if you stand up too quickly. "Low blood sugar levels from not eating for so long could cause problems," says Dr. Hu.

He suggests aiming for a 16/8 schedule, but take a gradual approach. For instance, first try a 12/12 schedule, where you eat during a 12-hour window and fast for 12 hours. "Follow this for a few days to get used to the schedule, and then extend the time to 14/10," says Dr. Hu. "When you feel ready, move to 16/8."

Intermittent fasting is not a quick weight-loss solution, so don't expect to immediately see or feel changes. "It can take a while for the practice to translate to lost pounds," says Dr. Hu. "Generally, people tend to lose about half a pound to one pound per week. Still, slow and steady weight loss is more successful and sustainable over the long term."

Dr. Hu adds that while intermittent fasting may help jump-start weight loss, a healthy eating strategy is necessary for success. "Any benefit you may gain from fasting won't last if you aren't eating healthy foods, controlling portions, and reducing your intake of snacks and processed foods."

Also, be mindful that intermittent fasting takes discipline, and you must stick with it to see any long-term benefits.

"You can't follow it now and then and expect any significant changes," says Dr. Hu. "But if you get off schedule for a day or two, you haven't negated your efforts. Just pick it up again and keep going. Eventually, you may see intermittent fasting become a part of your everyday life."

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