Intermittent Fasting for Beginners

Intermittent fasting has gained a lot of popularity in recent years as a strategy to lose weight, improve metabolic health, and even increase longevity. But what is it really? Is it as effective as it is made out to be? Let’s break it down so you can understand its types, benefits, and most importantly, whether it really offers advantages compared to other ways of eating.

What is intermittent fasting?

Intermittent fasting is an eating pattern in which periods of fasting (without eating) alternate with periods of eating (during which all of the day’s calories are consumed). Unlike traditional diets, fasting focuses less on what foods to eat or how much to eat, and more on when to eat them.

The concept of fasting is not new; it has been part of human history for centuries, whether for religious or cultural reasons, or simply because food was not as accessible in the past as it is today. What has changed now is that intermittent fasting has become a popular tool for weight loss and improved health.

Types of intermittent fasting

There are several ways to practice intermittent fasting. Here I’ll explain the most common ones:

1. 16/8 method This is probably the most popular type of fasting. It consists of fasting for 16 hours and eating during an 8-hour window. For example, if the first meal of the day is at 12:00 pm, the last one should be before 8:00 pm. You may also come across 18/6 or 20/4 fasts, which follow the same dynamic, except that the eating window is shorter.

1. 5:2 fasting This method involves eating normally for 5 days a week, while on the other 2 days calories are reduced to around 300–600. It is not a complete fast, but it is considered a way of intermittently restricting calorie intake.

• OMAD fasting (One Meal A Day) As its name indicates, this involves eating just one meal a day. It is a more extreme version of 16/8 fasting, in which the eating window is much smaller, typically one hour. 

Claimed benefits

If you go on social media, you’ll see that intermittent fasting is on everyone’s lips, being touted as a before-and-after turning point for many people’s health. Some of the benefits attributed to it are:

1. Weight loss and reduced body fat Without a doubt, the best-known benefit of intermittent fasting is weight loss. The theory tells us that by reducing the number of hours in which we can eat, we are more likely to consume fewer calories, creating a calorie deficit and, consequently, losing body fat. Indeed, this theory has been confirmed by several studies in which 16/8 fasting protocols cause people to consume fewer calories per day and lose fat (1-3)
2. Improved insulin sensitivity Some research suggests that intermittent fasting may improve insulin sensitivity, reducing the risk of diabetes or even being used as a treatment for this population group (4-6).
3. Increased growth hormone (GH) During fasting, growth hormone levels increase significantly. This hormone is related to the process of lipolysis, or in other words, the process by which stored fat is released into the bloodstream to be used as an energy source. Nevertheless, many fasting advocates claim that this hormone will also help them increase muscle mass, an assertion that lacks evidence. Building muscle mass is a very energy-intensive process, so it will never increase in a fasted state.
4. Improvements in metabolic health In addition to its effects on insulin sensitivity, intermittent fasting may reduce triglyceride, LDL cholesterol, and other markers of cardiovascular disease risk.
5. Cognitive benefits Some animal studies suggest that intermittent fasting may have neuroprotective effects, helping to maintain brain health and memory. Although human studies are limited, this could occur due to anti-inflammatory mechanisms.
6. Longevity Research suggests that intermittent fasting could extend lifespan in animals, although results in humans are not yet conclusive. The hypothesis is that fasting activates cellular repair processes that may help combat aging.

The reality of intermittent fasting: Is it really different?

So far, everything sounds great, but this is where I want you to pay attention. Most of the benefits attributed to intermittent fasting are due to the calorie deficit, not to a specific metabolic advantage of fasting itself. Let me explain.

When you reduce the number of hours in which you eat, it is easier to create a calorie deficit because you simply have less time to consume food. If you eat fewer calories than your body needs, you will lose weight, whether you follow intermittent fasting or eat 4 or 6 meals a day. There is no metabolic magic here.

When we look at many of the studies that attribute benefits to fasting, we realize that the subjects lose body weight, which is why improvements are seen in health markers such as cholesterol, insulin, or blood pressure. However, what happens when we compare them with the group that eats 4–5 meals but is in a calorie deficit? We achieve the same results as with intermittent fasting (7).

Conclusion: Is intermittent fasting for you?

Intermittent fasting is not a magic wand for losing weight. It is a tool that can help you organize your eating and, for many people, make eating less easier.

Some people may find it very convenient because they wake up and only feel like having a coffee, while for others breakfast is the highlight of their day. In both cases, what and how much you eat will matter much more than when you eat. If intermittent fasting makes you less hungry during the day, go ahead and keep it as part of your daily routine. However, if you have goals that require a high calorie intake (as is the case for endurance athletes or people looking to gain muscle mass), intermittent fasting may not be the best strategy.

In short, intermittent fasting may have additional benefits for some people, but most of its positive effects come from one simple thing: eating less. If you achieve the same calorie deficit by eating 4 meals a day, go ahead. The key is to find the eating pattern that best suits you, that you can maintain in the long term, and that allows you to enjoy food while achieving your health goals.

References:

1. Huang, L., Chen, Y., Wen, S., Lu, D., Shen, X., Deng, H., & Xu, L. (2022). Is time-restricted eating (8/16) beneficial for body weight and metabolism of obese and overweight adults? A systematic review and meta-analysis of randomized controlled trials. Food science & nutrition, 11(3), 1187–1200. https://doi.org/10.1002/fsn3.3194
2. Sukkriang, N., & Buranapin, S. (2024). Effect of intermittent fasting 16:8 and 14:10 compared with control-group on weight reduction and metabolic outcomes in obesity with type 2 diabetes patients: A randomized controlled trial. Journal of diabetes investigation, 15(9), 1297–1305. https://doi.org/10.1111/jdi.14186
3. Moro, T., Tinsley, G., Bianco, A., Marcolin, G., Pacelli, Q. F., Battaglia, G., Palma, A., Gentil, P., Neri, M., & Paoli, A. (2016). Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of translational medicine, 14(1), 290. https://doi.org/10.1186/s12967-016-1044-0
4. Albosta, M., & Bakke, J. (2021). Intermittent fasting: is there a role in the treatment of diabetes? A review of the literature and guide for primary care physicians. Clinical diabetes and endocrinology, 7(1), 3. https://doi.org/10.1186/s40842-020-00116-1
5. Yuan, X., Wang, J., Yang, S., Gao, M., Cao, L., Li, X., Hong, D., Tian, S., & Sun, C. (2022). Effect of Intermittent Fasting Diet on Glucose and Lipid Metabolism and Insulin Resistance in Patients with Impaired Glucose and Lipid Metabolism: A Systematic Review and Meta-Analysis. International journal of endocrinology, 2022, 6999907. https://doi.org/10.1155/2022/6999907
6. Albosta, M., & Bakke, J. (2021). Intermittent fasting: is there a role in the treatment of diabetes? A review of the literature and guide for primary care physicians. Clinical diabetes and endocrinology, 7(1), 3. https://doi.org/10.1186/s40842-020-00116-1
7. Elortegui Pascual, P., Rolands, M. R., Eldridge, A. L., Kassis, A., Mainardi, F., Lê, K. A., Karagounis, L. G., Gut, P., & Varady, K. A. (2023). A meta-analysis comparing the effectiveness of alternate day fasting, the 5:2 diet, and time-restricted eating for weight loss. Obesity (Silver Spring, Md.), 31 Suppl 1(Suppl 1), 9–21. https://doi.org/10.1002/oby.23568

Sergio Espinar