Intermittent fasting — to skip or not skip breakfast?

Intermittent fasting is getting very popular and for good reason. It entails consuming all of your calories in a specific time window, and not eating outside that window. A 16–8 protocol, for instance, would involve eating all your food in an 8-hour time frame, then not eating or drinking anything with calories, in other words ‘fasting’, for the other 16 hours of the day.

A common approach people use to fast is to skip breakfast. Many people find it to be pretty easy to simply have a cup of coffee or tea when they wake up and then wait to eat until lunch. If you ate dinner the night before at 8p, then waited to eat again until noon the following day, you would have fasted for 16 hours.

Breakfast skipping and fasting

If you’re like me, you probably grew up hearing that breakfast is the most important meal of the day. But where did this idea come from? And does science support it?

Researchers have observed that people who eat breakfast tend to be leaner and healthier. But skeptics point out (rightly) that people who eat breakfast, vs. those who don’t, are more likely to be nonsmokers, more physically active, consume less alcohol, and generally eat a better overall diet. So maybe the health attributes of breakfast eaters are simply due to healthier lifestyles.

Fortunately, there has been a large controlled trial that set out to determine what’s really going on here. In the Bath Breakfast Project, researchers took 33 men and women and compared the effects of eating and not eating breakfast for six weeks. They measured body weight, daily caloric intake, and a variety of metabolic markers. This way, they could tell how much these people were eating, how much energy they were burning, and the long term impact on weight.

It turns out skipping breakfast did indeed reduce the number of calories that these subjects ate every day. But, unfortunately, they didn’t lose weight because they were also less physical activity.

Not only is skipping breakfast disappointing for weight loss, it also decreases sensitivity to the hormone insulin, and worsens blood lipids. These ill effects are intensified when people skip breakfast and lunch to eat only one big meal in the evening. For example, people eating one vs. three meals per day (with same total calories, same food) had higher blood pressure, higher cholesterol, and greater hunger.

No bueno.

Does this mean intermittent fasting is a bad idea?

As indicated earlier, fasting is gaining popularity and for good reason. A number of exciting health effects associate with different fasting regimens, including increases in lifespan. One way fasting exerts it magic is by triggering a process called autophagy. Once activated, the autophagy process gobbles up pathogens, broken proteins, and other stuff that interferes with the proper functioning of our cells. In fact, this process is so important to our health that the 2016 Nobel Prize in Medicine was awarded to Yoshinori Ohsumi for his work on autophagy, and fasting is the natural way to initiate this important process.

So, how do we reconcile the findings that occasional fasting is healthy but breakfast skipping seems not to be (especially since intermittent fasting is fundamentally a meal skipping strategy)?

Timing matters

In the lab, when mice are only allowed access to food for 8 hours a day, there are a whole host of health benefits: lower body fat, lower cholesterol levels, and higher insulin sensitivity. It’s worth noting, however, that these beneficial effects are seen if that 8-hour eating window is during the time when the animals are normally awake and active. In contrast, when the shortened eating window is limited to a time when the animals are usually sleeping, they experience greater weight gain, worse blood sugar control, and other bad health effects.

And we see this in humans too.

In a controlled trial, overweight women who consumed more of their daily intake earlier in the day had greater improvements in blood sugar and lipids than those who ate more food later in the day.

Participants in the big breakfast group also lost, on average, 17.8 pounds and shaved 3 inches off their waistline, compared to 7.3 pounds and 1.4 inches for their big dinner counterparts.

Why this happens isn’t entirely clear. You’ll remember from the Bath Breakfast Project that I discussed above that eating earlier in the day seemed to stimulate more daily physical activity. Additionally, diet-induced thermogenesis (the increased metabolic rate that follows eating and drinking) is greater earlier in the day. Further research will hone in on th specifics of these impressive effects.

A better way

Even if you aren’t skipping breakfast, a shortened eating window still looks like a good idea. If you choose to intermittently fast, consider assigning most of your food intake early in the day, rather than trying to cram your calories later in the evening. In other words, instead of eating between 1–9pm, shift your window closer to the morning, like 9am-4pm.

In this way, you can enjoy the benefits of intermittent fasting, while eating in a way that is more metabolically advantageous. And if you want to learn more about intermittent fasting and meal timing, please check out our team’s ongoing series, which covers the subject in more detail.