Essentials: Effects of Fasting & Time Restricted Eating on Fat Loss & Health

Huberman Lab Essentials episodes, as the host describes them, revisit past episodes "for the most potent and actionable science-based tools for mental health, physical health, and performance." This installment focuses on intermittent fasting — aka time-restricted feeding — and its proposed influence on an unusually broad list of outcomes: weight loss, fat loss in particular, muscle maintenance and loss and gain, organ health such as gut health and liver health, the genome, the epigenome, inflammation, sickness, recovery, and healing from sickness, exercise, cognition, mood, and lifespan. Andrew Huberman, a professor of neurobiology and ophthalmology at Stanford School of Medicine, opens by conceding that the subject is one of the most contested in all of nutrition.

"If ever there was a topic that is controversial, especially on the Internet, it is that of diet and nutrition."

To anchor the discussion, Huberman cites a 2018 JAMA paper led by his Stanford colleague Chris Gardner, a 12-month weight loss study comparing a healthy low-fat diet with a healthy low-carbohydrate diet containing significantly more dietary fats. The paper, in which Gardner is first author, is presented as a landmark precisely because of what it found — and what it did not.

"there was no significant difference in weight change between people following a healthy low-fat diet versus a healthy low-carbohydrate diet with significantly more dietary fats in them"

The result "caused a lot of ripples in the world of nutrition and nutritional science, and certainly in the general population," because many readers assumed it must mean one macronutrient profile beats another. Huberman's reading is more careful: "This study was focused specifically on fat loss and on weight loss," so it cannot settle whether low-fat and low-carbohydrate diets differ on other health parameters. That distinction — what a study measured versus what people want it to prove — becomes a recurring theme of the episode.

The "calories out" side of the equation, in Huberman's account, is shaped by factors that a bare "calories in, calories out" slogan hides: - Amount of exercise and type of exercise both change daily energy expenditure. - Basal metabolic rate — how much energy one burns just sitting there — varies between individuals. - NEAT (non-exercise induced thermogenesis): people who bounce around and fidget a lot "can burn anywhere from 800 to 2,000 calories per day," so their effective basal metabolic rate is much higher, whereas more stationary people have a lower basal metabolic rate on average.

Hormones sit on the same side of the ledger. Thyroid hormone, insulin, growth hormone, and the sex steroid hormones testosterone and estrogen "will also profoundly influence the calories out, the calories burned component of the calories in, calories out equation." Huberman rejects two opposite internet slogans — that "Calories in, calories out does not matter" and that "Calories in, calories out is the only thing that matters" — arguing instead that there are foundational truths such as calories in, calories out, while insisting that hormone factors, and the context in which a given diet regimen is taking place, are exceedingly important.