Effects of Fasting and Time-Restricted Eating

How intermittent fasting actually works: most people don't understand the mechanism

Everyone already does some form of intermittent fasting (they sleep), but specific feeding schedules can impact health in different and powerful ways.

"Most people are familiar with the term intermittent fasting, but I think most people don't really understand how that process works."

Same calories, different outcomes: time-restricted mice stayed lean while ad-lib mice got obese

Mice eating the same high-fat diet and calories within a restricted window maintained weight, while those with 24-hour access became obese and sick.

"But nonetheless, everything I'm going to tell you is true also for humans, and we know this now from human studies. One of the most important things to take away from the study was that mice that ate a highly palatable, high fat diet, a great tasting diet, but only during a restricted feeding window of each 24 hour cycle, maintained or lost weight over time. Whereas mice that ingested the same diet, same amount of calories, but had access to those calories around the clock, gained weight, became obese and quite sick."

An 8-hour eating window during daytime aligns with circadian gene expression

The 8-hour feeding window reinforces circadian clock gene expression when combined with light exposure. Eating should happen during your active phase.

"And how long should that eating window be? Should it be eight hours? We already heard why the eight hour window was first established. It was because of these lab conditions and the conditions of the particular relationship of the graduate student involved, or should it be seven hours or six hours or 12 hours? Turns out that there's some general frameworks that we can follow in order to answer these questions. As we move into this portion of the discussion, I want to highlight a very important reference that just came out, literally came out last week in the journal Endocrinology Reviews. And the title of this review is Time Restricted Eating for the Prevention and Management of Metabolic Diseases. Although the data in this paper go well beyond metabolic diseases. This is a paper from Sachin Panda's lab. It's a very lengthy review with an enormous table that's beautifully organized that scripts out all the studies done in humans, well over a hundred studies, looking at time restricted feeding in athletes, men, women, children, diabetes, no diabetes, et cetera, with detailed references and description of the outcomes. I've spent a lot of time with this review, even though it just came out recently, and is a absolute gold mine resource. It is also the major resource for everything I'm about to tell you, if you would like to delve deeper into the material. So let's deal with this first question of when is the ideal feeding window? And here again, we're thinking about a schedule of eating that involves eating at least once every 24 hours, not two day or three day or every other day fast."

Best eating windows: noon-8pm is good, but earlier is better for fat loss

Attaching your eating window to your sleep-based fast makes it easier. A noon-8pm window is practical; earlier windows may have metabolic advantages.

"However, you're starting to taper into a fasted state before sleep and then all through sleep and until the next morning and late morning, you are actually in a fasted state. Now, most people find it very hard to only eat in the middle of the day. So while that's best, it's ideal for sake of the fasting related improvements in health. It is not ideal and it's not very applicable to most work and family and social situations. Most people eat breakfast with others and or eat dinner with others. Some people eat lunch with others, but in general, it's hard to restrict your feeding window to just the absolute middle of the day. But from a purely health perspective, in a very objective way, that would be the ideal situation."

HIIT during fasted state accelerates the transition into fat oxidation

High-intensity interval training while fasted can accelerate the metabolic shift toward fat burning and amplify the benefits of time-restricted.

"A fairly recent study looked at HIIT training, high-intensity interval training, which can take many different forms."

Eating = cell growth mode; fasting = cell repair mode (mTOR vs. AMPK/sirtuins)

Any food intake activates mTOR and cell growth pathways. Fasting or low blood glucose activates AMPK and sirtuins for cellular repair.

"Anytime you eat any food, doesn't matter if it's plant-based, animal-based, fat, protein, carbohydrate, doesn't matter. You are biasing your system towards a biochemical state of cell growth. And anytime you haven't eaten for a while or blood glucose is low, you're biasing your system toward a state of cellular repair. And this is why people who do not suffer from any blood glucose regulation issues, take things like berberine as glucose disposal agents or take metformin. I'm not necessarily suggesting that you do that, but it's because those things mimic fasting. They create situations in the body that promote things like AMPK and the sirtuins and others to push your body and your system down a route of repair, even though you might've just eaten a meal an hour ago. Along the lines of the health benefits of intermittent fasting, there are nice data showing improvements in the gut microbiome and in particular in the treatment of irritable bowel syndrome and other forms of colitis in time-restricted feeding. Meaning time-restricted feeding seems to be able to assist people with those conditions following the general parameters that I discussed before eight hours and so forth. Why and how? Well, by way of intermittent fasting impacting the expression of these various clock genes, and because the clock genes impact the mucosal lining, the mucus lining of the gut, it appears that intermittent fasting can reduce the amount of so-called lactobacillus that's present in the gut."

Time-restricted eating in elite cyclists: reduced cortisol, maintained performance

An RCT on elite cyclists showed time-restricted eating significantly reduced serum cortisol without hurting performance, and also improved gut.

"They had significant reductions in serum cortisol as a consequence of time-restricted feeding."

Glucose disposal agents: metformin, berberine, and even cinnamon mimic fasting

Compounds that lower blood glucose can push the body toward repair pathways even after eating. Artificial sweeteners are individual-dependent.

"Cinnamon is even a mild glucose disposal agent. It can actually reduce blood glucose."

Finding your ideal eating window: some people thrive with later windows (noon-8pm or 2-10pm)

The best feeding window varies by individual. Some do better eating later in the day, but always leave a 2-3 hour buffer before sleep to maximize.

"Some people tend to fall into a category where they do best placing that feeding window later in the day, provided it doesn't run too close to your sleep."