Intermittent Fasting – When to Eat

We’ve been advised to eat every two hours for the last couple decades in the name of keeping blood sugar stable and “not too low”. In recent years, however, the concept of Intermittent Fasting has come into favor for everyday people looking to stay healthy, maybe lose a few pounds, and for athletes looking for a competitive edge. So, what exactly is Intermittent fasting and is it right for you?

What is Intermittent Fasting?

Intermittent fasting, or what I prefer to call it, intermittent eating, is based upon the idea that we don’t need to eat every two hours, and in fact, constant eating and snacking may be harmful to your health.

When we eat, there are several normal hormonal changes that occur. Perhaps the most notable is the release of insulin (the amount released is partially based upon the composition of our food). One of insulin’s jobs is to prevent the breakdown of current stored energy and help us store excess energy from a meal that we cannot immediately use.

In the case of carbohydrates, the bulk of calories in the American diet, they mostly break down into glucose during digestion. Some of this glucose energy will be taken up by tissues that currently need energy (mostly by our muscle), but the excess needs to be stored for later use by the liver as either glycogen (chains of glucose) or stored as fat tissue through de-novo lipogenesis.

Our bodies are always in flux between using energy from what we’re eating and using stored energy. This is a good thing so we have energy overnight while we sleep! The goal of taking time off eating is to allow insulin to come down rather than being constantly elevated, which allows us to utilize some of our stored energy.

For someone with normal insulin sensitivity and liver function, the liver will breakdown stored glycogen to keep blood sugar stable when we’re not eating (such as overnight), and can even create glucose when we’ve run out of glycogen.

In addition to allowing us to tap into stored energy, intermittent fasting has been shown to have multiple benefits including:

The great news is that intermittent fasting doesn’t require caloric restriction, and can be as simple as having 16 hours between dinner and breakfast (think dinner at 6pm, breakfast at 10am).

Make sure you discuss your intermittent fasting goals with your physician to make sure it’s appropriate for you or if there’s certain things you should monitor while fasting.

Daily Fasts

Daily fasts can last anywhere between 12 hours to 20 hours. If you ask your grandparents, it’s likely they ate family dinner at 5pm, finishing by 6pm, and didn’t eat again until breakfast around 7am. That’s a 13 hour fast with no effort and no intentional caloric restriction.

Today’s modern work schedules, snack environment, and reduced sleeping hours often mean we eat dinner late in the evening and snack between dinner and bed. If you only sleep for 6-7 hours and eat as soon as you wake up for work, you likely had 8 hours or less of fasting, very different from your grandparents. Five hours might not seem like much, but this lack of time tapping into stored energy every single day can take a toll on our metabolic health. Why are we storing energy if not to use it later?

For optimal digestion, sleep, and lipid metabolism, don’t snack between dinner and bed and aim for a minimum of 4 hours between finishing dinner and going to sleep (while still getting a good night’s rest). The combined 4 hours after dinner and 8 hours of sleeping is already 12 hours of fasting.

Condensed Eating Window

The shorter your eating window, the more important it is to plan your meals for adequate daily nutrient intake. You can also alternative your eating windows throughout the week. Perhaps you eat more meals with family on the weekends and only fast 12 hours overnight, but on busy workdays, perhaps your eating window in smaller. This variation allows for the benefits of fasting without rigid requirements that interfere with social activities and your overall happiness.

The eating window you set can be based on practicality such as eating dinner with your family or your work schedule, but it can also be set to optimize fat burning, called fat oxidation. We know from metabolic ward studies that when calories and physical activity are held constant, how we use vs store energy is impacted by when we eat. Fat oxidation and insulin sensitivity are higher in the morning than at night when our bodies are preparing for sleep. Subjects fed earlier in the day burned more body fat than subjects fed later, and this is with the same food, same calories, and same physical activity. This is known as the circadian regulation of lipid metabolism.

Extended Fasts