Volume 106: Fasting - Is It Right for You?

My work focuses on mental health, gut health, and metabolic health. You already know from reading this newsletter that each one of these influences the others. Not surprisingly, there are lots of nutritional and integrative interventions that can support healing these systems. I address one of them in this newsletter thanks to a reader’s question: fasting.

You can’t swing a short stick without hitting a podcast or news article about fasting. The data is pretty compelling - but is it right for everyone? I dig into pros and cons, and also provide viewpoints on fasting that often get left out.

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Reader's Question:

“I would love to know more about fasting. It is promoted strongly by some of my favorite podcast sources, and I appreciate the idea of more "metabolic rest" especially for menopausal women, but I find fasting to be stressful, headache inducing, and maybe not worth the benefits.”

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Fasting is one of the darlings of the nutrition world.

The evidence promises health improvements across the body via a very straightforward, free-to-use route: simply don’t eat periodically for an extended period of time. The research literature supports this intervention.

Certain models of intentional fasting have demonstrated routinely improved: blood glucose levels, insulin sensitivity, use of fat for energy, weight management, mitochondrial health/energy production, brain health, and mood; and a decrease in inflammation, cancer cell proliferation, oxidative stress, cardiovascular disease, and mental illness.

So much to like, right?

I would be remiss in not pointing out that some form of fasting is an ancient ritual in each of the world’s five major religions. Those who participate report a remarkable feeling of lightness and being closer to their higher power. Often this is a water fast, limited food over a day(s), or a dawn to dusk fast, as in Ramadan, and typically it is in combination with prayer and other religious practices.

How is fasting done?

Just so you are in on the lingo, in the medical and nutrition worlds “fasting” means a period of time of not eating. “Fed” or “feeding” indicates times of consuming food and the post-consumption metabolism of it. So in research, they distinguish between a “fasted state” and a “fed state” for a subject. A “feeding window” indicates how many hours a day are designated as available for food consumption.

At the American Nutrition Association summit in October, I heard a compelling presentation by Sebastian Brandhorst, PhD of the Longevity Institute on the role of fasting in healthy aging. Spoiler alert: fasting supports longevity. He defined the primary forms of intentional fasting this way:

• Calorie Restriction (CR): reduction of total caloric intake of the standard diet by 15-40% for a limited feeding window. This is the form most weight loss diets take.
  
• Time Restricted Feeding (TRF): short feeding window of between 4 to 12 hours without calorie restriction. This, I think, is what most of us think of as Intermittent Fasting, and the terms are often used interchangeably.
• Intermittent Fasting (IF): alternate 24 hours fasting/24 hours feeding, using the standard diet without calorie restriction.
• Periodic Fasting (PF): 1-2 days fasting followed by 6-5 days feeding, using the standard diet without calorie restriction.
• Fasting Mimicking Diet (FMD): reduced caloric intake to ~30% of energy needs for 5 days with a specifically defined, nutritionally supportive diet that reduces protein intake as well as calories, then a post-FMD return to the standard diet. There is no feeding window. Performed from once a year to quarterly to monthly.
• Water Fast: Consuming only water for anywhere from 24 hours to 3 days.
  

Dr. Brandhorst highlighted Time Restricted Feeding (TRF), Intermittent Fasting (IF), and Periodic Fasting (PF) as the most effective, sustainable fasting techniques, with TRF as the most accessible. Most people, even nutrition professionals, think of TRF as interchangeable with IF as a term. I use TRF here since it is the most accurate to what most people follow.

Time Restricted Feeding

A TRF feeding window can be as narrow as 4 hours to as long as 12. TRF follows circadian light/dark rhythms - eating during the day and not overnight. The last meal is no later than early in the evening, and the next meal is taken sometime after waking the next day. This provides the body time to focus on tending to itself: sweeping out metabolic trash, repairing, rejuvenating, and building, which is what it does during the quiet hours of night and sleep.

A second longevity expert, Dr. Kara Fitzgerald, whose life work researches healthy aging using food and lifestyle, points out that the benefits of TRF can be reached with a mere 12 hour stretch of not eating between dinner and breakfast. Finish dinner at 7:00pm, and eat again as early as 7:00am. Voilá! You have done time restricted feeding.

Some choose TRF daily, and others insert limited feeding windows a few times a week. It’s a flexible method that can be individualized. Dr. Brandhorst described that there are many benefits to TRF. One is that humans are social, and social factors influence when we eat. TRF days and timing can be chosen by the individual and so can be socially adapted. A key point is that TRF does not restrict calories. The health benefits echo the ones described in my first paragraph, with the bonus elements of an improved quality of life, higher energy, more restful sleep, and lower hunger at bedtime. In short, TRF enhances both lifespan and healthspan.

What could go wrong?

Going to my reader’s question, TRF, especially with a longer fasting window, can be a trigger for those who have low blood sugar or suffer from migraines. Those who suffer from chronic stress, including the stress and energetic drain of poor sleep, also may feel worse trying TRF. During these times, the body requires more support nutritionally and regular energy inputs. Remember that lengthy periods of fasting or highly calorie restrictive diets can deplete nutrients, even with refeeding. Too short a feeding window can prevent consuming the amount of food/nutrients (both macro- and micronutrients) that our bodies need. If you are already consuming the minimal amount of calories your body needs to function well (a form of mild CR), adding TRF may tip into damaging instead of health promoting.

TRF can undermine our health if we don’t start with a foundational food plan that is nutritionally rich. A body that already experiences nutritional deficits will suffer rather than improve, especially as a fasting window is widened. On top of that, most who feel deprived on a fast (especially CR) are more likely to react with a binge - either because their body is desperate for easy energy or because they feel psychologically isolated from the pleasure of food - or both. Pregnant and nursing people should not participate in TRF - or any fasting - due to the need for regular energy and nutrient intake.

If you want to try TRF, choose the least limited fasting window of 12 hours and see how it goes. Widen the fasting window gradually (or don’t!) to find your own sweet spot. Remember that TRF does not need to be daily or even weekly, and you don’t need to choose it at all.

What else should I know about fasting?

There’s one concern I always have about any program that restricts food in any form: could it trigger health issues, a disordered relationship with food, or an eating disorder?

The fewest health benefits and the biggest risk comes from extreme calorie restriction (CR). Dr. Brandhorst explained that it does not provide lasting benefits for weight loss or cardiovascular disease. In fact, he rather dryly pointed out that starving animals live longer - unless it’s overdone and they die.

Too many commercial weight loss diets involve a form of CR fasting that ultimately results in muscle wasting and nutrient depletions. They are unsustainable and eventually fail those who try them, often triggering new health problems, disordered eating, body distrust, and eating disorders. I suspect this topic is of interest to many, so I will happily explore it more deeply in another newsletter.

From my viewpoint, any fasting program has the opportunity to lure the participant into ever more extreme versions of itself, especially with promises of weight loss or the new shiny object - living long past 100. This is a significant disordered eating/eating disorder risk factor especially for tweens, young adults, and - surprise! - middle aged women.

Take-Home Message

Well managed Time Restricted Feeding can be an incredible way to shape our health for the better.

• 12 hours of fasting overnight provides all the health benefits.
• It is typically safe, easy, and effective to increase the fasting window up to 14 hours, if desired.
• Feel free to extend the fasting period longer if you feel good doing it, but it’s not necessary.
• Be sure to include adequate calories and nutrition during your daily feeding window.
• Do not restrict calories.
• Aim for mostly nutrient dense meals, and remember that we eat for pleasure as well as physical nourishment. Include fun foods and celebratory foods.
• Those who suffer hypoglycemia, headache/migraine, or other health issues may not be good candidates.
• Pregnant and nursing women should not fast in any form.
  

If you become rigid and rules-based about what you are eating and when, and if not following those rules upsets you, you feel that you need to restrict and/or compensate for breaking your rules, and/or you find yourself routinely eating until overfull or binging (especially common later in the day/evening), it’s critical that you work with a nutritionist and therapist who are disordered eating/eating disorder informed practitioners.

A key point of any eating plan is tuning in to how it makes your body feel. If it’s not working, become aware of what’s not right for you so that you can make choices that help you feel most well.