Intermittent Fasting May Improve Metabolic Health, a Small Study Finds

Time-restricted eating was associated with a reduction in LDL cholesterol, blood pressure, A1C, and abdominal fat.

Restricting the window in which you eat may help stabilize your blood sugar and keep your heart healthy.Shutterstock; iStock (2)

Is it possible to improve your health not by eating less, but instead by simply shaving a few hours off your daily eating window? A small but promising new study suggests that restricting eating to 10 hours a day over a three-month period can lead to weight loss, a reduction in belly fat, and improvements in many risk factors that can lead to early death. The study, published in December 2019 in Cell Metabolism, included people diagnosed with metabolic syndrome, a term for several different conditions at once, including hypertension, high blood sugar, high cholesterol, and excess abdominal fat.

Although researchers didn’t stipulate what foods or how many calories to consume, participants ate an average of 8.6 percent fewer calories over the course of the three-month period, and lost 3 percent of their body weight and 4 percent of their abdominal fat. “We are excited about these results, in large part because time-restricted eating can be so widely adopted in clinical practice,” says co-first author Michael Wilkinson, MD, an assistant clinical professor of medicine at the University of California in San Diego and a cardiologist at UC San Diego Health.

Time-restricted eating is just one type of intermittent fasting. Other options include 5:2 fasting, where you eat normally for five days and restrict calories to 500 or 600 on the two other days, and alternate-day fasting, where you restrict calories to about 500 every other day.

A doctor doesn’t necessarily need extra training in diet or nutrition to recommend time-restricted eating to patients, says Dr. Wilkinson. “It’s fairly easy to explain and for people to adopt,” he says. “In this study we allowed people to choose their own 10-hour window for eating, which they were able to build into their daily routine,” he adds.

Time-Restricted Eating: So Simple It Just Might Work

To see what impact eating for fewer hours a day would have on people with metabolic syndrome, investigators recruited 19 people: 13 men and 6 women. All the participants took part in time-restricted eating; there was no placebo group. The majority of the participants were on a statin to reduce cholesterol, a medication to reduce blood pressure, or both. Before the study began, the average eating window for the participants was more than 14 hours a day.

With time-restricted eating, you’re only allowed to consume calories during certain hours, according to the American Heart Association. A typical window of eating time could be 8, 10, or even 12 hours.

In the two-week period before the study began, researchers had the subjects record what and when they ate using myCircadianClock, an app that can help track daily eating, sleeping, and activity patterns. The app is free to download on Google Play and the App Store.

One strength of the study was the granular information on the timing of eating it provided, says Deborah Wexler, MD, an assistant professor at Harvard University and the clinical director at the Massachusetts General Hospital Diabetes Center in Boston. Dr. Wexler was not involved in this research. “It is notable at baseline [before the study began] that many participants were ‘grazing’ over the course of the day and part of the night, with one participant eating for 17 hours in a 24-hour period,” notes Wexler. This is likely a common eating pattern in the United States today, she adds, and it can lead to excess calorie consumption.

All the participants chose to begin their 10-hour window between 8 a.m. and 10 a.m., and end between 6 p.m. and 8 p.m. On the basis of food-consumption records collected before the study began, researchers concluded that the participants didn’t skip breakfast, but instead delayed it for an hour or two. The same went for dinner: Rather than skipping the meal, people ate their final meal earlier to accommodate the schedule. When they weren’t eating, participants were encouraged to drink water. Using the myCircadianClock app, each individual logged what and when they ate, as well as their sleeping times.

There were no adverse events reported. After the three-month trial, not only did the patients lose weight and fat, but their “bad” LDL cholesterol and blood pressure dropped too. Blood sugar and insulin levels began to improve as well, showing better metabolic health.

“The high-risk population that this study included — people with metabolic syndrome with mild class one obesity — makes up a large part of the population in the United States,” says W. Scott Butsch, MD, the director of obesity medicine in the Bariatric and Metabolic Institute at the Cleveland Clinic in Ohio, who was not involved in this research. According to the latest data from the National Health and Nutrition Examination Survey (NHANES), more than one-third of all American adults meet the criteria for metabolic syndrome. 

“We know that people with metabolic syndrome are five times more likely to develop diabetes and two times more likely to develop cardiovascular disease,” says Dr. Butsch. “The short-term improvements in the components of metabolic syndrome achieved by narrowing participants’ eating period from about 14 to 10 hours is very encouraging,” says Butsch. If further research confirms these findings, healthcare professionals may consider recommending time-restricted eating to improve their patients’ health, he adds.

Time-restricted eating is simple to explain and relatively easy for patients to understand and adopt, says Wilkinson. “Not only was compliance high throughout the study, many participants continued to practice time-restricted eating even after the study was over,” he notes. “They received no instructions to do so, but many people liked the changes they saw and the way that they felt at the end of the study period,” says Wilkinson.

Improvements in Cholesterol and Blood Pressure Independent of Weight Loss

Although weight loss typically leads to drops in LDL cholesterol, the participants’ levels went down significantly more than expected, which could indicate that time-restricted eating offers additional health benefits. “By adding time-restricted eating to the standard medical care and medications they were already taking, it had a dramatic effect on improving the targeted end points,” says Wilkinson.

According to the National Lipid Association recommendations for the management of dyslipidemia, a 5 percent loss in body weight should produce a 3 to 5 percent reduction of LDL cholesterol. In this study, although the participants lost just an average of 3 percent of their weight, their LDL went down 11 percent.

Blood pressure also dropped significantly. Triglyceride levels, which would be expected to go down with weight loss, did not change. The investigators also observed trends toward improvement in fasting glucose, and among participants with elevated fasting blood glucose, there was a significant reduction in hemoglobin A1C.

The benefits go beyond what would typically be expected with the amount of weight the subjects lost, says Wilkinson. Although it’s not clear what’s causing the additional improvements, it could be the effect that time-restricted eating has on metabolism, which is linked to circadian rhythms, he says. “All organs in the body rely on internal circadian clocks for healthy metabolism; one hypothesis is that by better aligning dietary intake with those normal circadian rhythms, we’re actually seeing a healthier metabolism,” says Wilkinson. For example, it could potentially make the medicine that the subjects take for their cholesterol more effective, he says.  

Additionally, there are some emerging data that the time of day when people take medications can influence their efficacy, says Wilkinson. A study published in October 2019 in the European Heart Journal found that if patients with high blood pressure took their medication at bedtime rather than when they woke up, it improved their blood pressure and markedly reduced the number of major heart events. Wilkinson speculates that perhaps the timing of medications when combined with time-restricted eating could potentially have a synergistic effect. “It’s not something we can answer with this study, but it warrants further investigation,” he says.

Next Steps for Evaluating Time-Restricted Eating

Wilkinson and colleagues are already performing a related study using time-restricted eating in participants with metabolic syndrome. “This is a bigger trial, and it’s a randomized controlled study, so we’ll have a control arm, which will be a standard of care diet,” says Wilkinson. “That will give us more information about all the effects of time-restricted eating.”