The Fuss About Intermittent Fasting

Intermittent Fasting As A Recent Trend

It is no secret that we are in the throes of an epidemic of obesity. Currently over 22 states have more than 35% of their population classified as obese, whereas ten years ago, no state had an obesity prevalence at or above 35%. The majority of all weight loss programs eventually fail, with two-year follow-ups showing more than half the weight loss was regained, and at five years more than 80% regain everything (initial success is defined as losing at least 10% of initial body weight, so in addition we have early failures).

The last five years have brought about an intense interest in Intermittent Fasting (IF), or more appropriately, Time Restricted Eating (TRE). Originally, the anecdotal experience was that IF might be more effective for weight loss than other methods such as counting calories or restricting certain classes of food. Recent studies have focused on potential improvements in metabolic health, blood pressure, lipids, and Hemoglobin A1c.

What Exactly Do We Mean by “Intermittent Fasting”?

Although the common definition of fasting means abstaining from food or drink, the term “Intermittent fasting” is vaguely defined, even in medical studies, varying in meaning from the overnight fast (starting when dinner ends until first meal of the following day), to the extreme “OMAD,” or one-meal-a-day eating plan. There are even IF plans where patients eat every other day. There is an important distinction between “early” intermittent fasting, where eating ends around 3 pm, or “late” IF where we skip breakfast and start eating later in the day. These varying schedules can have very different results, in terms of physiological effects, outcomes, and whether weight loss is mainly fat, or both fat and muscle.

Every week I have at least one patient showing up to an appointment stating that they practice intermittent fasting. However, upon questioning, I find out they mean that they no longer eat in the evening after dinner, and they often have an early AM coffee, and have moved their breakfast from 8 am to 10 or 11 am. In addition, many are adding collagen, almond milk, butter or MCT oil to their coffee. Once you have added more than five calories, you have officially broken the fast. IF is one end of a pendulum… we have become a society that regularly eats in our car, eats at our desk, and eats in front of the television in the evening. Therefore, NOT eating after dinner might feel like we are practicing some sort of “fast” or restriction but in fact, many who say they are doing IF are simply skipping breakfast.

What Do Clinical Studies on Intermittent Fasting Show?

As of early 2024 there have been about 15-20 small, short-term, randomized trials of TRE/IF (see the recent meta-analysis referenced below). Overall, for weight loss, there has been a slight, some would say not impressive, advantage to the TRE schedule. It should be pointed out that ALL of the studies that showed a positive trend for weight loss with IF also used enforced CALORIC RESTRICTION along with time restriction, so participants were coached or voluntarily ended up employing a 500-calorie restriction as well as a time restriction.

Many, actually most, of the studies used a schedule called “early” TRE, meaning everyone ate breakfast and lunch and stopped eating at 3 pm. The Liu study (referenced below) was criticized because it ended up with only a 2 to 3-hour difference in eating window. Despite the difficulty of abstaining from dinner, most participants were able to be compliant 5-6.5 days out of 7.

One troublesome finding: some of the studies showed an overall small advantage to TRE in weight loss but not fat loss, meaning in a few studies there was more significant muscle loss in the TRE group vs. the straight calorie-reduced group (see the Lowe study below). This muscle loss is problematic, as we already are losing muscle with aging, and loss of more muscle will lower our metabolic rate, contributing to weight regain once we are not strict with the program.

If you study centenarians, they consistently eat breakfast but finish eating early, around 7 pm. They do not deprive their body of food during the day when they are out and about. We don’t have any two-year or five-year follow-up to know that this weight loss will stick better than the programs that came before it. We also don’t know the long-term effects. In one sense, fasting during the daylight hours while you are exercising, working, driving, or generally more active, places a stress on the body and the organs, which can elevate cortisol, adrenal hormones, and cause tissue breakdown. We are asking our liver, our muscles, our heart, and our brain to work well during a time when no minerals, dietary antioxidants, or macronutrients are coming in. We simply don’t know the long-term health effects of this type of chronic stress on our bodies.

Is What I’m Doing Actually Intermittent Fasting?

Most people who say they are doing IF are actually not doing it in the way that it was studied. They are not imposing a specified caloric reduction, they fast during the morning and noon hour rather than after four pm (or they actually don’t fast at all, because they are putting butter or collagen in their morning coffee) and they are not strict (six out of seven days). In addition, when they are losing weight using IF, they are not tracking where the weight is coming off, using whole body DEXA or BIA to gauge fat or muscle loss and making the necessary corrections to their protein intake. They are not tracking their thyroid and sex hormones to see if there is evidence of excessive stress in the body. In short, it’s a little bit of the “wild west” out there, with many people following influencers rather than the medical science studies.

Intermittent Fasting Best Practices

There definitely are some for whom time-restricted eating is helpful. It allows insulin and glucose levels a longer time to drop. It works as a way to reduce calorie intake without excessive hunger or a complete makeover of the shopping and cooking habits. That lack of change is precisely the reason that it may not work forever, and may not be the optimal way to lose weight. There are dietary challenges with IF that might be better handled using Flexible Dieting plans (see our blog on Flexible Dieting) such as inadequate protein to support muscle fiber synthesis, not enough diversity of vegetables over the week, not enough fiber or hydration, or an excess of ultra-processed snacks or foods. Also, it is very important to track muscle mass on any weight loss diet where there is more than 5% body weight lost. Tracking can be done accurately on an InBody BIA machine or Whole Body Dexa.

In short, intermittent fasting is not a magic bullet and will likely result in a plateau, as all plans do that reduce calories by more than 400-500 calories per day. At Hudson Valley Longevity Medicine we focus on optimal body composition in our Fitness for Longevity Package, where we construct a personalized diet strategy that fits your needs and goals. For more information check out our website and if you think you’re ready for a personalized fitness plan that plants the seeds for a long and healthy future, schedule an appointment today.

References

Effectiveness of Early Time-Restricted Eating for Weight Loss, Fat Loss, and Cardiometabolic Health in Adults With Obesity: A Randomized Clinical Trial – Jamshed H, Steger FL, Bryan DR, et al. JAMA Intern Med. 2022;182(9):953–962. doi:10.1001/jamainternmed.2022.3050 https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2794819

Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial – Lowe  DA, Wu  N, Rohdin-Bibby  L,  et al. JAMA Intern Med. 2020;180(11):1491-1499. doi:10.1001/jamainternmed.2020.4153 https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2771095

Calorie restriction with or without time-restricted eating in weight loss – Liu  D, Huang  Y, Huang  C,  et al. N Engl J Med. 2022;386(16):1495-1504. doi:10.1056/NEJMoa2114833 https://www.nejm.org/doi/10.1056/NEJMoa2114833

Time-restricted eating with calorie restriction on weight loss and cardiometabolic risk: a systematic review and meta-analysis – Jing-Chao Sun, Zhen-Tao Tan, Chao-Jie He, Hui-Lin Hu, Chang-Lin Zhai & Gang Qian European Journal of Clinical Nutrition: Meta-analysis: IF WITH caloric restriction can be metabolically favorable but long-term effects remain to be explored (most studies are very short term). Lots of low-quality small studies. No longer term trials. https://www.nature.com/articles/s41430-023-01311-w