Time restricted feeding

Skipping Breakfast May Raise Risk of Heart Disease!!! screamed the recent headline. There were similar variations on that theme all over Main Stream Media. So if you get your diet factoids from headlines, you might conclude that

  • eating breakfast prevents heart disease OR
  • skipping breakfast causes heart attacks

Or both. You’d be wrong on both counts. To their credit, the actual scientists who did the study came to no such conclusions. They realized that breakfast eating was part of the lifestyle that raised heart disease risk. Smoking, lack of exercise, unhealthy snacking and overconsumption of alcohol were common for breakfast-skippers. So simply adding breakfast to your unhealthy lifestyle isn’t going to improve health.

Breakfast skipping is actually promoted by certain celebrities and diet gurus as a weight loss strategy. They might want to pay attention to a different concept: chrononutrition:

the interaction of daily metabolic rhythms, time of day and food intake impacts body weight, blood glucose and other health indicators

You might have heard of the 16:8 Diet, which is a play on this idea. 16:8 refers to hours in the day. You’re supposed to compress your food intake into an 8-hour span, say 10 a.m. to 6 p.m. and eat nothing at all for the other 16 hours. Meaning, you fast from 6 p.m. until 10 a.m. the following day.

The concept is attracting research attention, since there is evidence that human metabolism is influenced by the so-called circadian clock. Researchers typically refer to this idea as Time Restricted Feeding (TRF), meaning the span of time during the day when you’re allowed to “feed” is restricted.

One study looked at the effect of TRF on a small group of people of varying body weights. Half the group ate normally for 10 weeks. The other half was instructed to move the first meal of the day ahead by 1-1/2 hours and the last meal back by 1-1/2 hours from their typical eating pattern. In other words, not strictly a 16:8 schedule for everyone; rather the person’s usual feeding window was cut by a total of 3 hours. A person who used to eat breakfast at 8 a.m. and finish dinner by 7 p.m. was now asked to wait until 9:30 for breakfast and to be finished with dinner by 5:30.


  • The TRF group spontaneously reduced food intake. In other words, they were not told to cut back on food. It just happened as a side effect of restricting the hours they could eat.
  • Despite eating less, they did not lose significant weight. However, keep in mind, these were not necessarily over weight people to begin with.
  • All of the TRF group lost body fat. This is pretty interesting, considering they didn’t weigh much less.
  • There was one significant drawback: sticking to the TRF timeframe. Several of the subjects said it was hard to do, because social engagements, illness, work and family commitments meant eating outside the time restriction.

Another study examined the effect of the 16:8 diet on obese people. This group was told to eat only between 10 a.m. and 6 p.m. for 12 weeks. The subjects ate 350 fewer calories per day, even though they were not told to restrict food intake. They lost weight and had lower blood pressure. This sounds promising as a weight loss strategy, since people don’t have to count calories, or feel like they’re being deprived.

Again, the TRF group had trouble with sticking to the plan. Most did not follow the 16:8 schedule perfectly, but they got better at it as the study went along.

Here’s a variation on the breakfast theme. In this study obese women were put on 1400 calorie diets. Half of them ate half the calorie allowance at breakfast and just 200 calories at the evening meal. The other half ate 200 calorie breakfasts and 700 calorie dinners. Everyone ate 500 calories at lunch.


Everyone lost weight, but the large breakfast group lost more 2.5X more weight and had more significant improvements in waist size, BMI, blood glucose, insulin, triglycerides and several other measurements. 2-1/2 times more weight loss on the same calorie intake! That’s pretty impressive. Maybe there’s something to that breakfast claim after all.

Take Aways

There’s nothing particularly magic about the 16:8 idea. What seems to be important is a prolonged period everyday, probably more than 12 hours, when you consume nothing besides water. You could do 14:10 or 15:9. The point is to give your digestive system and metabolism a chance to reset.

What can we conclude about the time restricted feeding idea? If weight loss is your goal, it seems to work. Food intake may be reduced, but there also seems to be an effect on how the food is handled. These and other studies suggest that the greatest impact is on body fat, with additional benefit for body weight and disease risk factors.

There are a few reasons not to try this sort of diet: diabetes, pregnancy or breastfeeding, or use of medications that must be taken with food. It’s not a good choice for a child or teen. And definitely a bad idea for someone with an eating disorder, as it just encourages restrictive behaviors.

Given the evidence, you might decide to try time restricted feeding, but life gets in the way, as many study subjects found out. Don’t feel defeated. You might manage to stick to the schedule 5 days a week, or 4. Maybe 16:8 turns into 13:11 sometimes. You do the best you can under the circumstances.

What these studies don’t tell us is anything about diet composition. Would TRF work if you ate nothing but junk food? Even if true, I don’t recommend that. Would it work even better if you were eating a plant-based diet? Maybe.

Interestingly, the TRF studies all left room for breakfast. In fact, the study subjects were advised to eat 3 meals a day. Certainly, if you’re following the 16:8 plan, you’ll be hungry at 10 a.m., since you haven’t eaten for 16 hours. So in a way, time restricted feeding encourages breakfast. And if a lifestyle that includes breakfast helps prevent heart disease, so much the better.

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