Nutrition Notes

New Research on Time-Restricted Eating

According to data from the Centers for Disease Control and Prevention (CDC), over 100 million adults in the US are living with type 2 diabetes or pre-diabetes, and nearly 35 percent have metabolic syndrome. (This proportion rises to nearly 55 percent when looking specifically at those aged 60 or older.) Metabolic dysregulation and the comorbidities that travel with it are a national health crisis. It will take more than platitudes like “eat less, move more” and “everything in moderation” to have a meaningful impact on this alarming situation. We’ve previously covered the impressive efficacy of ketogenic diets and general carbohydrate restriction in helping to improve blood sugar control and insulin resistance in people with type 2 diabetes. However, reduced carb diets are only one approach, and not everyone is interested in going this route. For these individuals, time-restricted eating is an alternative tool in the arsenal that may be effective for improving cardiometabolic health even in the absence of a significant dietary change.      

Research published last month in the journal Cell Metabolism adds more data to the growing body of literature supporting a role for time-restricted eating (TRE) as an intervention for individuals with metabolic syndrome. The paper’s title sums it up succinctly: “Ten-Hour Time-Restricted Eating Reduces Weight, Blood Pressure, and Atherogenic Lipids in Patients with Metabolic Syndrome.” The study was small—just 19 subjects—but it’s worth looking at, especially considering human trials of TRE are limited so far. (Most of the research has been done in animals.)

The subjects were diagnosed with metabolic syndrome, and most were taking a statin drug for cholesterol and/or medication for hypertension. Their habitual eating pattern was to consume food for greater than 14 hours per day, leaving less than 10 hours to be in a fasted state. According to the author of the Satchin Panda, Ph.D., most subjects had previously tried conventional methods to improve their health, such as lower calorie diets and increased exercise.  

The intervention called for 12 weeks of consuming all usual foods and beverages within a 10-hour timeframe, giving them a 14-hour fasting period. (Drinking water and taking medications were permitted during the fasting period.) Subjects were free to choose a timeframe that best suited their work-family life, so the precise timing was not mandated, only the total number of hours of eating and then abstaining from food. During the last two weeks of the study, subjects wore a continuous glucose monitor and activity monitor.

The results were encouraging. On the whole, subjects lost weight (particularly abdominal fat, for a smaller waist circumference), had reduced blood pressure, lower LDL and non-HDL cholesterol, lower HbA1c, and reported more restful sleep. And this was accomplished with no change in physical activity. Regarding caloric intake, it would be natural to assume that going a few hours longer without consuming any food would automatically result in a substantial reduction in calories, but researchers found that subjects decreased their caloric intake by only a “modest” 8 percent, and they did not find a strong association between this reduction and the measured improvements in health. (This echoes earlier findings from multiple studies that significant cardiometabolic improvements can occur even in the absence of weight loss. Examples of such research include a study of TRE in men with prediabetes, and a study comparing very low carb diets to moderate and high carb diets in subjects with obesity and metabolic syndrome.)

Dr. Panda ad co-author Pam Taub pointed out that TRE removes some of the complexity and difficulty of micromanaging calories, carbs, fat, or energy expended during physical activity. For people with neither the time nor the inclination to track their food and activity, TRE may be a viable alternative that could deliver results without these obstacles. Improving parameters of metabolic syndrome may have more to do with when people eat than what they eat.

A study from earlier in 2019 by some of the same researchers involved middle-aged men with obesity who were at risk for type 2 diabetes. Subjects were instructed to consume their usual diet but were restricted as to when they could eat: in one part of the study, they ate between 8 am and 5 pm; in the other part, they ate between 12 pm and 9 pm. So both parts had a 9-hour eating window, with 15 hours of fasting. (Water, mints, gum, and non-caloric beverages were permitted during fasting hours to improve compliance.) The TRE was only done for a week but even in that short time, there was a major improvement in glucose and insulin response to a test meal after both experiments. Fasting blood glucose levels improved only after the early eating window (8 am-5 pm), but fasting glucose may be less important than the postprandial glucose excursion, and this was improved in both timing interventions. The amount of time spent not eating is what was responsible for the effect, not the timing of when food was consumed. As Dr. Panda wrote, “Timing is the medicine.”

The Cell Metabolism study had notable weaknesses, including its small sample size and single-arm design. But it was a feasibility study, intended as a starting point. Dr. Panda acknowledged that “more rigorous randomized control trials and multiple location trials are necessary next steps,” and plans are already in place for a clinical trial, expected to be completed in 2023. This study will add even more to the scientific literature on TRE and fasting, which is growing quickly. We previously reported on substantial improvement in type 2 diabetes after a fasting protocol, and improvements in cardiovascular risk markers along with reduced fat mass even among healthy, non-obese adults.

Time-restricted eating and various permutations of fasting appear to be highly promising for improving metabolic health even in the absence of weight loss. This is noteworthy because of the growing population of individuals with “normal weight obesity”—those who are not overweight yet have cardiometabolic profiles aligned with metabolic syndrome and high risk for cardiovascular disease, not to mention individuals with full-blown type 2 diabetes who are not overweight.  

A parting word of caution: TRE and intermittent fasting may not be appropriate for everyone. They appear to be powerful interventions for a number of purposes but there are numerous other effective strategies. Limiting the timing of food consumption is simply one tactic to consider alone or in conjunction with other therapies when warranted for an individual’s circumstances and goals. Individuals who are taking medication—especially for hypertension or diabetes—must be monitored closely upon adopting TRE or intermittent fasting because dosage adjustments may need to be made quickly.