Is the answer to the question of what to eat… to eat nothing at all?
Advice for what to eat, when to eat, and how to eat can be confusing and conflicting. I’ve talked to many people that say the amount of nutrition information out there tends to be more overwhelming than helpful. When this happens, it seems easier to simply eat nothing at all than navigate these muddy waters. It’s for this reason that intermittent fasting often seems so appealing. Proponents of intermittent fasting will proclaim the amazing benefits of simply not eating, saying that fasting will make you leaner, stronger, smarter, and even live longer. Are these claims true? Let’s find out!
If you’ve never heard of it, intermittent fasting is a dietary approach that involves abstaining from food for a particular period of time. There are many different forms that intermittent fasting, but the most popular forms are time-restricted feeding and alternate-day fasting. Time-restricted feeding includes a prolonged period of fasting followed by a shorter eating, or “feasting” period. This can often look like a 16-hour fast with 8 hours to eat, an 18-hour fast with 6 hours to eat, or a 20-hour fast with 4 hours to eat. On the other hand, alternate-day fasting involves eating little to no food for an entire day, while other days involve unrestricted intake.
Of course, one of the first things that come to mind with fasting is fat-loss. During a normal eating schedule, the average person eats enough food to provide their body with a consistent supply of energy. The body converts nearly all food to glucose, the body’s preferred energy source. At the same time, the body is able to store some glucose in the muscles and liver as glycogen. This stored energy is there for when you are pushing through intense exercise or go a short period without eating. When you don’t eat for 12 hours or more, though, you begin to drain your glycogen storage. Around the 16-hour mark of no food, give or take, is where the body is out of glycogen and forced to switch to fat-burning. The body is extremely efficient as storing fat (to many people’s dismay) because it wants to tap into using it for energy when food is sparse. This metabolic shift occurs to make the body no longer rely on glucose, but instead use its own stored bodyfat as fuel. To do so, your body breaks apart stored fat and turns it into ketone bodies, or ketones. These ketones circulate in the blood for readily available energy, and they are actually the namesake for the ever-popular “Keto diet”. The ketogenic diet is a whole other conversation, but this diet shares a similar process to intermittent fasting. It is by this mechanism, though, that intermittent fasting has become very famous for burning fat. Truly, there is a variety of research backing intermittent fasting’s ability to aid people trying to leaning out.4 The effect of fat loss with fasting is multiplied with endurance exercise, or cardio. Endurance exercise classifies as longer duration and usually lower intensity. Exercises like jogging and biking would qualify. With this type of exercise, your body actually prefers to burn fat for energy. If you do cardio in the fasted state, your body has already started liberating stored fat and converting it into ketones. As you jog, your working muscles are happy to pick up the fat and ketones circulating in the blood and burn them for energy.4 How can you practically apply this to your own fat-loss journey? If you are able to fast overnight and exercise before breakfast, cardio in the morning will have your body burning fat much more efficiently than after breakfast or any other meal of the day. It’s worth noting these effects aren’t a magic bullet, though. Fat-loss doesn’t happen overnight. Even if you were fasting during that night! There is limited research saying that people didn’t lose fat using intermittent fasting,3 but this research was done over a short period of time and in a very small group of people. In the end of the day, being consistent with your exercise and nutrition will always be the key to leaning out.
What about those of us that care more about living longer? Some research has related intermittent fasting to a variety of general health benefits that fight some of the most common ailments leading to death and disease. Some research has found that intermittent fasting has helped improve cholesterol levels, protect heart health, improve the balance of gut bacteria, and even help to fight cancer. Limited research saw that intermittent fasting actually decreased peoples’ triglycerides and LDL (bad cholesterol), while increasing their HDL (good cholesterol). Further, different fasting regimens have been found to slow down cell proliferation (excessive growth), decrease inflammation, and reduce hormones that are indicated in uncontrolled growth of cells. All of these processes are related to the belief that fasting can help prevent certain forms of cancer. In the gut, the metabolic changes that occur with fasting influence the “good” and “bad” bacteria. In short, fasting has been seen to increase the good and decrease the bad bacteria, which is a piece in improving digestion and gut health, as well as even helping to reduce and fight obesity. Part of these benefits from intermittent fasting stem from the ability to help the body reconnect with its circadian rhythm. The circadian rhythm is the body’s internal clock, telling us when to sleep, wake up, eat, exercise, and much more. Our current lifestyle that involves unpredictable eating and sleeping patterns disrupts the body’s circadian rhythm, causing improper brain and hormone signals and patterns. Providing the body with set times to eat, fast, and sleep helps realign this rhythm and can correct the body’s metabolism. In doing so, our ability to regulate our bodyweight, fight cancer, and generally stay healthy is vastly improved. Further, there’s some research beginning to suggest that a properly executed intermittent fasting regimen can even help reduce stress and improve learning abilities.1,2,4
What about working out? Won’t fasting hurt my performance in the gym? Well… it might. Generally, exercise performance during “feasting periods”, or the times that you can eat, is unaffected. Unfortunately, a good number of studies has found that individuals that exercise during their fasting periods usually perform worse.4 In other words, intermittent fasting might help you lean out faster, but you most likely won’t be able to lift any heavier or run any faster. The evidence doesn’t suggest your workouts will be worse, they just won’t likely be any better.
How would you know if intermittent fasting is worth trying? Intermittent fasting may be achievable and sustainable if you’re someone who finds that they “forget to eat” when they’re too busy, has a work/life schedule that makes eating or snacking more difficult, or finds that they simply “don’t get hungry” very often. With lifestyles like this, intermittent fasting may be an easy dietary pattern to adopt. When you don’t feel like eating or don’t have time to eat, just don’t eat! On the other hand, intermittent fasting may not be sustainable if you’re someone who gets very tired or “hangry” from not eating, quickly gets hunger pains, or has better energy levels when they snack on small meals throughout the day. If you’re an individual in the latter group, you might feel like there’s no hope for reaping the benefits of intermittent fasting. Fear not! Even shorter periods of fasting carry their own benefits. Research has found that simply eating dinner at a normal time, say about six o’clock, and not eating the rest of the night until breakfast can have health benefits. Fasting between dinner and breakfast could help improve your quality of sleep and even help regulate blood sugar levels for the whole next day.5 Both of these benefits can lead to sustained energy levels for the entire day, prevent you from feeling the need to overeat, and prevent fat storage during the day. Even if fasting for 16 hours seems quite daunting, refraining from some late-night snacking can impart benefits similar to intermittent fasting without all the hunger pains.
Whew! There’s a lot that has to do with “not eating”! What’s the moral of the story? Intermittent fasting is simply another approach to how we eat, and it may have certain health benefits if you find it to be sustainable. Just as important as how we eat is what we eat, though. Regardless of how you approach nutrition, what matters most is that you eat a balance of food that is good for you and that you enjoy. Food is fuel, true. But food is also emotional. Food is tradition. Food is social, and food is meant to be shared and enjoyed. So, whether you’re slurping a kale smoothie or splitting a pizza, rest assured that you’re living a healthy life if you’re enjoying what you consume without allowing it to consume you.
- Longo VD, Mattson MP. Fasting: molecular mechanisms and clinical applications. Cell Metab. 2014;19(2):181-192. doi:10.1016/j.cmet.2013.12.008
- Patterson RE, Laughlin GA, LaCroix AZ, et al. Intermittent Fasting and Human Metabolic Health. J Acad Nutr Diet. 2015;115(8):1203-1212. doi:10.1016/j.jand.2015.02.018
- Tinsley GM, Butler NK, Forsse JS, et al. Intermittent fasting combined with resistance training: effects on body composition, muscular performance, and dietary intake. J Int Soc Sports Nutr. 2015;12(Suppl 1):P38. Published 2015 Sep 21. doi:10.1186/1550-2783-12-S1-P38
- Zouhal H, Saeidi A, Salhi A, et al. Exercise Training and Fasting: Current Insights. Open Access J Sports Med. 2020;11:1-28. Published 2020 Jan 21. doi:10.2147/OAJSM.S224919
- Wagner S. Diabetes. Medical Nutrition Therapy II; March, 2020; University of Wisconsin-Green Bay, Green Bay, WI.