By David Prince, MD | Montefiore Medical Center

Although new GLP-1 agonist weight loss drugs such as Ozempic, Wegovy, Trulicity, and Byetta are currently dominating the headlines, the majority of overweight Americans may not qualify for these medications due to limited availability and insurance plan restrictions. This means established recommendations regarding nutrition and physical activity will have to guide most Americans to a healthy body mass index. For some, intermittent fasting is a viable option.

Endorsements from celebrities such as Jennifer Aniston and Hugh Jackman, alongside recommendations from nutritionists and doctors, created a buzz around intermittent fasting as a hot health and wellness trend before the GLP-1 agonists captured the imagination of the world as dietary control in a pill. As the name implies, the method involves alternating between periods of eating and fasting. The duration varies from person to person and can be as short as skipping breakfast or as long as eating during a one-hour interval every 24 hours, also known as the “OMAD” diet.

Intermittent fasting has many of the same benefits of the GLP-1 agonists — including weight loss and improved metabolic markers — which is logical, as the main effect of GLP-1 agonists is to reduce appetite and increase the feeling of fullness with smaller portion size. As more people explore intermittent fasting, the scientific community has responded with a growing body of research. This article summarizes some of the growing literature to highlight the benefits and potential drawbacks of this popular technique.

Brain Health and Cognitive Function

Emerging evidence suggests that intermittent fasting can support brain health and enhance cognitive function. Animal studies¹ have shown that fasting can stimulate the production of brain-derived neurotrophic factor, a protein that supports neuron growth and protects against neurodegenerative diseases. Human studies, although limited, also suggest potential cognitive benefits. Reduced oxidative stress might slow brain aging and could theoretically reduce the risk of neurodegenerative conditions like Alzheimer’s.² Circadian rhythms are often disrupted in this disease, so it stands to reason that patients with Alzheimer’s may benefit from improved synchronization of circadian rhythms that come with time-restricted eating.³

Longevity and Disease Prevention

Animal studies have shown that intermittent fasting offers numerous health benefits that could be interpreted as protective against age-related decline.⁴ Fasting activates pathways that enhance cellular repair, reduce oxidative damage, and promote autophagy, all potentially contributing to increased longevity.

In humans, long-term studies are still needed to conclusively determine the impact of intermittent fasting on lifespan. However, preliminary data is promising. For example, a review article in the New England Journal of Medicine describes the numerous benefits of intermittent fasting beyond weight loss, including improved cellular function and resistance to stress and reduced inflammation.⁵

Potential Drawbacks and Considerations

While intermittent fasting offers numerous health benefits, it is not for everyone. Almost everyone experiences side effects such as fatigue, irritability, and difficulty concentrating during fasting periods — especially at the beginning. People prone to low blood sugar either from medications or any other cause, pregnant or breastfeeding women, and those with a history of eating disorders should discuss with their primary medical provider before starting an intermittent fasting regimen. Anyone who has a reduced ability to sense when their blood sugar is low should not attempt fasting without medical supervision.

Patients’ Experience

Personal anecdotes are often of greater interest than scientific studies. Enthusiasts of intermittent fasting, myself included, have described it as a journey through the “Valley of Hunger.” Many start by simply eliminating one high-caloric food item that they are consuming too frequently. (For me, it was potato chips!) Every patient knows what they’re eating too much of — just ask them. It’s important to choose something that isn’t very difficult to give up, ideally something being eaten automatically and without thought — e.g., salty snacks, small candies. Once patients realize it’s actually not difficult to make a small change, they can consider eliminating breakfast once a week and continue to build from there. Checking in with them is important for encouragement and support as well as monitoring. Most find that although they are hungry, they gain a greater sense of control over their eating patterns. It’s important to meet people where they are when it comes to fasting. It is so contrary to our culture and basic education — the importance of three meals a day is embedded into modern society.

One benefit of intermittent fasting not often discussed is that there is no preparation and no cost. Intermittent fasting saves time and money. A tremendous amount of effort and preoccupation with what we’re going to eat consumes much of the average person’s day. When it comes to managing hunger and cravings, the most important thing is to remain hydrated (which means anyone with fluid restrictions falls into a patient population that should not be fasting). Recommendations include always making sure varying drinks are on hand: morning tea, coffee in the afternoon, flavored water and seltzer throughout the day. All of these are very helpful in preventing mild dehydration from being mis-perceived as hunger. Lastly, it’s important to not feel deprived; this only leads to discontent and is not sustainable. If someone really wants to eat something, it is better to acknowledge that and move on. They can always make it up the next day or skip the next meal as compensation.

Conclusion

Intermittent fasting works for some people to improve their health and assist in weight loss or weight management. The scientific evidence supports its benefits in metabolic health, cardiovascular health, brain function, and potentially longevity — although this remains to be proven for humans. As with any dietary strategy, there must be customization based on individual preferences, medical conditions, and ability to tolerate fasting. Everyone should discuss this or any major dietary undertaking with their primary medical provider before making a significant change to eating patterns. It’s important to share this with the primary provider,  who will be observing the effects of fasting directly and, without appropriate context, will be unable to provide optimal primary care. As the medical literature matures around this topic, intermittent fasting may become a well-supported option for weight management. In the meantime, it is worth it to keep an eye on what is published in medical literature and to be able to discuss all dietary options with our patients.

David Prince, MD, is the Director of Cardiopulmonary Rehabilitation at Montefiore Medical Center in New York City and President-Elect of AACVPR. His interests include increasing access to cardiac and pulmonary rehabilitation throughout the healthcare spectrum. He is also an intermittent faster and (generally) eats one meal a day during the work week.

References

1. Mayor E. Neurotrophic effects of intermittent fasting, calorie restriction and exercise: a review and annotated bibliography. Front Aging. 2023 Jun 2;4:1161814. doi: 10.3389/fragi.2023.1161814. PMID: 37334045; PMCID: PMC10273285.
2. Cherif A, Roelands B, Meeusen R, Chamari K. Effects of intermittent fasting, caloric restriction, and Ramadan intermittent fasting on cognitive performance at rest and during exercise in adults. Sports Med. 2016 Jan;46(1):35-47. doi: 10.1007/s40279-015-0408-6. PMID: 26438184.
3. Dong TA, Sandesara PB, Dhindsa DS, Mehta A, Arneson LC, Dollar AL, Taub PR, Sperling LS. Intermittent fasting: a heart healthy dietary pattern? Am J Med. 2020 Aug;133(8):901-907. doi: 10.1016/j.amjmed.2020.03.030. Epub 2020 Apr 21. PMID: 32330491; PMCID: PMC7415631.
4. Strilbytska O, Klishch S, Storey KB, Koliada A, Lushchak O. Intermittent fasting and longevity: from animal models to implication for humans. Ageing Res Rev. 2024 Apr;96:102274. doi: 10.1016/j.arr.2024.102274. Epub 2024 Mar 17. PMID: 38499159.
5. De Cabo, R.(2019). Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine. 381(26):2541-2551. Doi: 10.1056/NEJMra1905136.