Meal window, not time, matters for health

So, you’ve decided to try out time-restricted feeding (TRF) and shorten your eating window to 10 hours or less. Should you start eating early with breakfast, or have lunch be your first meal?

It’s a good question, and one that hasn’t been directly investigated until today.^​1​ A study took a small group of 15 obese men and had them eat within a 9-hour TRF protocol starting either with breakfast (8–5 pm) or with lunch (12–9 pm). They did that for a week, took a 2-week break (washout period), and then did the other option for a week.

After just one week on each protocol, glycemic control to a test meal was improved regardless of when the eating window occurred. There were also no differences in average 24-hour blood glucose levels or glycemic variability.

There were also no differences between the protocols for changes in body weight, appetite ratings, total energy expenditure, physical activity, sleep duration, gastric emptying rate, gastrointestinal hormones (ghrelin, GLP-1, GIP, amylin, PYY), triglycerides, or free fatty acids.

Have breakfast and lunch or lunch and dinner; it doesn’t matter whether your feeding window is in the earlier part of the day or goes into the night when it comes to a variety of health outcomes.

These findings make sense in light of a study suggesting that the body “learns” its meal times and adjusts its metabolic responses to eating accordingly.^​2​ Specifically, glucose intolerance to lunch occurs only in people who regularly eat breakfast and decide to skip, it doesn’t occur in habitual breakfast skippers.

The body “learns” its meal times and will adjust its metabolic responses to eating in accordance with what we regularly do.

Time-restricted feeding is what matters

I’m tired of hearing people say that there are no benefits to TRF other than weight loss. Just stop, please.

We have a lot of data in animals that TRF prevents the development of cardiometabolic diseases,^​3​ and emerging research in humans is beginning to find similar benefits.^​4​

One of the best studies demonstrating the independent benefits of TRF is one involving men with prediabetes who had all their food provided to them to ensure that they didn’t eat less from restricting their feeding window.^​5​ It was shown that eating three meals within a 6-hour TRF window benefited glycemic control, insulin sensitivity, blood pressure, and oxidative stress compared to eating those same three meals within a 12-hour window.

A second study in resistance-trained men performed a similar investigation: Over an 8-week period, the men consumed equivalent amounts of food as three meals per day within an 8- or 12-hour window while following the same resistance-training program.^​6​ Both groups experienced small, similar increases in muscle mass and strength, but the 8-hour TRF group lost more body fat (-1.6 kg vs -0.3 kg) and saw minor improvements in markers of inflammation.

Obviously, simply having people reduce their eating window will tend to cause a reduction in calorie intake and body weight.^​7,8​ And this will lead to associated improvements in health like better sleep, less hunger, more energy levels, and reduced insulin resistance.^​7,8​

But dammit, there are benefits to TRF outside of weight loss. We have a handful of studies clearly demonstrating that.

Summing up

There are benefits intrinsic to time-restricted feeding that occur independent of weight loss. Eating within a 6–10-hour feeding window seems to provide a variety of health benefits compared to eating the same stuff spread out in a longer eating window of 12+ hours.

Whether this feeding window comes earlier in the day (breakfast and lunch) or later in the day (lunch and dinner) doesn’t seem to matter. The body isn’t stupid and appears to adapt to our regular eating schedule.

References