Time-restricted eating improves endurance, muscle, and fat loss


I’ve previously written about how time-restricted eating works with your body’s natural circadian rhythms to control your weight, improve insulin sensitivity, reduce inflammation, prevent diseases like diabetes and cancer, and extend your overall longevity. For those not interested in health and weight control (which is fine, I was once young and invincible too), I also plan to explain how time-restricted eating improves endurance and increases overall muscle mass.

Not all fasts are equal

A recent study concluded that intermittent fasting shows no benefits over traditional dieting. Since people have been forwarding me a lot of articles based off that study, I wanted to quickly address their conclusion first.

I’m not surprised the study didn’t show any difference because they missed the point on why intermittent fasting or time-restricted eating works in the first place. Humans are diurnal, which means we’re active during the day and asleep at night. To regulate this active / recharge cycle, your body relies on circadian rhythms to manage biological functions like cellular repair and hormone signaling. Certain functions like metabolism simply work better during the day than at night.

Most people have heard of melatonin. It’s one of the hormones your body uses to maintain it’s circadian rhythms on the sleep side of the equation. It’s also been shown to inhibit the release of insulin which means you are less able to process consumed sugar at night. In addition, your muscle cells are also on a circadian clock and they become less insulin sensitive at night. Not only do you make less insulin but your body stops listening to it so all the sugar you consume simply sits in your bloodstream causing damage. This has big impacts on your health and weight, but it also teaches your body to become less efficient at utilizing energy (which reduces endurance).

Since the above study doesn’t take time into account, they just conclude the point of intermittent fasting is to trick you into consuming less calories. Their results demonstrated that the normal diet group and the alternating-day fasting group (25 percent of energy needs on fast days; 125 percent of energy needs on alternating “feast days”) had similar results in weight loss and blood profile, so they assumed this “trick” worked just as well as a normal daily-restricted diet. Some minor details I found left out of most of the articles sent me was that the intermittent fasting group had a significantly higher drop out rate and a pretty low compliance rate. The researchers stated “participants in the alternate-day fasting group ate more than prescribed on fast days, and less than prescribed on feast days.” It seems like this fasting strategy was so unpleasant that people either quickly gave up or didn’t really stick to the plan at all (and that’s just based on what they admitted to the researchers).

As I mentioned previously in the time-restricted eating article, the reason it works has nothing to do with calorie-restriction or even food quality. It works because you only eat when your body is chemically ready to process it properly. Like with everything, a proper well-balanced diet will lead to even greater results, but I wanted to emphasize, that time-restricted diets can improve your health and weight regardless of calorie totals or diet quality.

Timing matters

Dr. Satchidananda Panda from the Salk Institute for Biological Studies in San Diego has been studying the effects of circadian rhythms on metabolism, gene expression and the immune system. My review in this article focuses on two mouse studies you can read about here and here and a human study you can find here. I’ll quickly summarize the studies first and then the results below that:

image Image from www.sciencedirect.com

  • Study 1: Two groups of mice were fed a high-fat diet and did not exercise at all. One group could eat whenever and the other group could only eat within a circadian-rhythm appropriate, 8-hour window. Calories were the same between groups.

  • Study 2: This mouse study was a bit more complex. Mice were fed one of four diets: high-fat, high-fructose, high-fat and high-sucrose, and regular mouse chow (the equivalent of a healthy diet). The groups were then further divided into feeding periods of 9 hours, 12 hours, 15 hours, or whenever they wanted. The study also experimented with allowing some mice to eventually have a “cheat weekend” where the time-restrictions were removed for two days. Others were moved from restricted groups to permanently non-restricted groups and vice versa. Calories were the same across all groups.

  • Study 3: This human study had people use an app to snap a picture of what they ate whenever they ate it. It allowed the researchers to get a realistic picture of the “feeding window” people naturally adopted. Once data on habits was gathered, some overweight participants were asked to switch to a 10 to 11 hour feeding window with no requirements on calorie restriction.

I’ll get into some additional interesting findings below but in general, every participant (human or mouse) on a time-restricted eating schedule either lost weight or was protected from weight gain (or both) regardless of diet quality or calorie totals. Additional findings:

  • Beneficial results of time-restriction occurred only at 12 hours and under. The 15-hour restriction was not effective.

  • The benefits of the time-restricted schedule were not harmed by the two-day “cheat weekend.” The researchers concluded that “the weekday time-restricted feeding imprints a gene expression signature that can resist occasional changes in the feeding pattern.”

  • Mice on the time-restricted obesegenic diets had 28 percent less total mass and 70 percent less fat than the unrestricted group.

  • Time-restricted mice had improved glucose tolerance and insulin sensitivity and an improved lipid profile.

  • Time-restricted mice had reduced inflammation and oxidative stress.

  • Time-restricted mice had increased mitochondria volume, especially in the liver and brown fat cells plus less damaged mitochondria (from oxidative stress)

  • Time-restricted mice had increased PGC-1 alpha levels which is the master regulator of mitochondrial biogenesis.

  • Young mice did respond more favorably to time-restricted eating than older mice, however in older mice, switching to a time-restricted schedule did reduce body fat by 20% and prevented further weight gain.

  • In the human study, participants believed they only ate 12 hours a day, but results showed the average window was actually 15 hours.

  • 35 percent of calories consumed in the human study were after 6 pm.

  • Participants in the human study that adopted a time-restricted feeding schedule reported no problems with compliance because they said it improved their sleep quality and provided more energy the next day.

The above results were independent of diet quality. In fact, the point of many of the test groups was to show the benefits of time-restriction when the diet was especially poor. Improved diet-quality in the second study led to additional fitness benefits in the mouse groups such as:

  • Increased lean muscle mass compared to normal chow mice on the unrestricted feeding schedule. The researchers don’t know why this happens yet and additional research is required, but they did notice elevated levels of NAD+ which is associated with protecting muscle mass, improved energy and longevity.

  • The 9-hour restricted group had significantly improved aerobic fitness. In the treadmill run-to-exhaustion test, the unrestricted normal chow group ran for 77 minutes while the 9-hour normal chow group ran for 141 minutes.

Time-restricted eating works with your body’s natural internal clock to improve your utilization of energy. In addition, damage from reactive oxidative species is only repaired in a fasted state. Improving recovery and the efficiency of energy usage will quickly improve your overall fitness. Just as I mentioned how fasted-training turns on fat-burning genes, time-restricted eating also influences positive gene expression. It could actually be another reason why the sleep low training strategy improves race times so significantly. The early morning workout pushes back the feeding window (as you’ll see below) which makes it similar to a time-restricted plan.

The clock starts when you consume anything

One of the things people don’t seem to understand is that your circadian clock is not set in stone. It responds to external stimuli like light and activity to make slight shifts that will better help match you to your environment. This is why exercise helps stabilize circadian rhythms and improve sleep quality and why too much artifical light at night interferes with your internal clock and disturbs sleep patterns.

Since one of the important functions of circadian rhythms is to regulate metabolism, it’s not surprising that when you eat also helps set your internal clock. When deciding what time-restriction to adopt for your own habits, realize that the clock starts as soon as you consume anything more than water. Even black coffee counts because it activates the clock in your liver to metabolize the caffeine. Anything that needs to be metabolized starts the clock, even if it doesn’t contribute any calories. This is the ultimate example of my advice to get your body’s chemistry working for you instead of against you. Studies have found time-restricted eating to be an easy yet surprisingly effective strategy to improve your health, prevent weight gain and contribute to weight loss. It also improves your sleep quality, daily energy levels, muscle mass, and even your aerobic fitness if you combine time-restricted eating with a proper diet.

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