Intermittent Fasting to Lose Weight: What the Science Says

It's no secret that intermittent fasting has become a popular weight loss strategy over the past few years. But is there any science behind it, or are people just jumping into another diet trend?

We're going to take a look at what the evidence says about using intermittent fasting for weight loss and if it's an effective and sustainable approach.

What is Intermittent Fasting?

Intermittent fasting is an eating pattern where you eat within a specific time frame each day and fast (or refrain from eating) for the rest of the time.

Typically, people will go a period of 16 hours without food (although it can be shorter or longer depending on your schedule) and then eat all their meals in an 8-hour window.

Because this eating pattern occurs on a 24-hour cycle, many people choose to schedule their fasts around their sleep schedule so that they don’t miss meals or snacks outside their eating window.

For example, you might eat all your daily meals between noon and 8 pm, with a 16-hour fast from 8 pm until noon the following day - essentially opting to skip breakfast.

Reversing that slightly, you could also opt to eat all of your daily meals between 8 am and 4 pm, with a 16-hour fast from 4 pm until 8 am the following day - choosing to skip evening meals like dinner.

The Types of Intermittent Fasting Protocols

There are various different approaches to intermittent fasting, each with pros and cons. Here are the most popular types of intermittent fasting protocols:

16/8 Method

The 16/8 method is the most popular type of intermittent fasting. It involves fasting for 16 hours and eating during an 8-hour window. For example, you would fast from 8 pm to 12 pm, and then eat meals between 12pm and 8 pm. This protocol is often called the “Leangains Method” as it was popularized by fitness expert Martin Berkhan.

5:2 Diet

The 5:2 diet is a type of intermittent fasting that involves eating normally for 5 days per week and restricting your calories to 500-600 for 2 days per week. Journalist Kate Harrison popularized this method in her book “The 5:2 Diet.”

Alternate Day Fasting

Alternate day fasting is a type of intermittent fasting that involves fasting every other day. On fasting days, you would consume only water or other non-calorie beverages. This method was popularized by journalist John Berardi in his book “The Metabolism Advantage.”

Warrior Diet

The warrior diet is a type of intermittent fasting that involves eating small meals during the day and then consuming one large meal at night. Fitness expert Ori Hofmekler popularized this method in his book “The Warrior Diet.”

The Best Intermittent Fasting Protocol

The best intermittent fasting protocol for you will depend on your lifestyle, goals, and preferences. Some protocols may be more sustainable, depending on your schedule and lifestyle.

For example, if you have a very busy work or school schedule, the 16/8 method may be better suited for you as it doesn't require drastic changes to your daily routine. If you have more flexibility in your schedule, the 5:2 diet or alternate-day fasting may be a better fit.

It is important to remember that meal timing is extremely individualized and should be allowed to be flexible.

If something is not working for you, feel free to adjust the plan accordingly or opt-out altogether.

Research shows that overall healthful behaviors are more important than specific meal timing when it comes to weight loss and long-term health outcomes. So, prioritize those health behaviors instead of obsessing over when you eat meals.

The Benefits of Intermittent Fasting

As a diet trend picked up by the biohacking community in recent years, there are several claims that it has several potential health benefits.

Weight Loss

The overall idea is that an intermittent fasting routine limits the amount of time you can eat each day and thus help reduce your daily caloric intake.

Cutting calories by fasting or reducing your eating window, this puts your body into a calorie deficit. This means that you are eating fewer calories than the number of calories you burn in a day.

This state of being in a calorie deficit encourages your body to start burning its stored fat for energy - leading to weight loss over time.

Studies have shown that intermittent fasting can help people lose body weight when done correctly. A 2023 systematic review of randomized trials found that intermittent fasting was as effective for weight loss as a typical low-calorie diet, with the bonus of being easier to maintain in the long term.

The key takeaway here, however, is that for intermittent fasting to be effective for weight loss, you still have to consume fewer calories than you burn. It's not a replacement for calorie counting.

Research indicates that fasting is not more effective than other calorie-restrictive methods. A 2022 study on intermittent fasting in the New England Journal of Medicine showed that fasting yields no difference in weight loss compared to caloric restriction.

A 2018 review of studies in the International Journal of Obesity had similar findings. The primary driver for weight loss is still a calorie deficit, and an intermittent fasting plan is just a tool or style of eating that can help you achieve that deficit.

Improved Insulin Sensitivity

One of the proposed intermittent fasting benefits is improved insulin sensitivity. Insulin is a hormone produced by the pancreas that allows our bodies to use glucose for energy. Insulin sensitivity refers to how well our cells respond to insulin and absorb glucose from the bloodstream.

When we become insulin resistant, our cells don't respond as well to insulin, which can lead to high blood sugar levels and eventually type 2 diabetes. This is where intermittent fasting can come into play - some research suggests that it may improve insulin sensitivity.

A study published in the International Journal of Endocrinology found that intermittent fasting can improve insulin sensitivity in healthy adults. The study measured insulin sensitivity before and after four weeks of intermittent fasting. The results showed that intermittent fasting improved insulin sensitivity and decreased insulin resistance.

Another study found that intermittent fasting improved insulin sensitivity in overweight men with prediabetes. The men had to fast for 16 hours each day and eat within an eight-hour window. After five weeks, their insulin sensitivity improved significantly.

So there is some evidence to support the claim that intermittent fasting can benefit insulin sensitivity. . But here's the million-dollar question - are the benefits solely related to meal timing, or are they related to fewer calories consumed overall?

A study published in Obesity Reviews argues that the benefits of intermittent fasting on insulin sensitivity may be due to calorie restriction rather than meal timing. The authors suggest that the weight loss and overall reduction in calorie intake during intermittent fasting may be responsible for improving insulin sensitivity.

It's also worth mentioning that the long-term effects of intermittent fasting on insulin sensitivity are not yet fully understood. While some studies have shown short-term benefits, whether these benefits are sustainable or will last in the long run has yet to be shown.

While intermittent fasting may have some potential benefits for improving insulin sensitivity, more research is needed to fully understand its impact on long-term health benefits.

Reduced Inflammation

Inflammation is a natural response of the body to injury or infection. Inflammation is a natural response of the body to injury or infection. However, chronic inflammation can lead to several serious health concerns such as metabolic syndrome, type 2 diabetes, and heart disease.

Now, when it comes to intermittent fasting, some studies suggest that it can reduce inflammation in the body.

One study found that short-term fasting can decrease certain cells called monocytes that cause inflammation. They also discovered that fasting can improve chronic diseases without affecting the body's ability to fight off infections or heal injuries.

Additionally, Yale Researchers found that a compound produced when dieting or fasting can block the immune system involved in inflammatory disorders like type 2 diabetes and Alzheimer's disease.

While some studies suggest fasting can decrease inflammation, it's still in the early stages of research.

I am not seeing research validating that fasting is more effective at reducing inflammation than we already know it does: eating a healthful diet.

Eating a healthy diet rich in antioxidants, fiber, healthy fats, and lean protein is already known to help reduce inflammation.

But wait, there's more! Stress is also a major factor in inflammation. When you're stressed, your body releases hormones that trigger inflammation. And if you're dealing with chronic stress, that can lead to chronic inflammation.

So, if trying to stick to an intermittent fasting protocol makes you feel stressed about your eating habits, then it might not be the best option.

Remember, intermittent fasting is just an eating style - it's not inherently healthy. Instead, focus on a balanced diet and reducing stress to reduce inflammation in the long run.

Increased Brain Function

Recent scientific studies suggest that intermittent fasting might positively affect the brain, making it stronger, more resilient, and better at fighting age-related cognitive decline.

Now, let's talk about the science. In one study, researchers found that intermittent fasting can increase the number of newly produced neural cells in rats and increase the expression of proteins associated with neurogenesis. This suggests that intermittent fasting may impact how the brain changes and ages.

Another study found that an intermittent fasting pattern can help the brain, but researchers aren't sure how. So they looked at mice to see how fasting affects neurogenesis (making new brain cells) and found that fasting for three months increased a signaling pathway called Notch 1 and other factors like BDNF and CREB. These findings suggest that intermittent fasting may promote the growth of new brain cells.

But what does this mean for the average person looking to improve their brain health? Is intermittent fasting the magic solution? Well, it's not quite that simple.

To start, these studies were done on rodents, not humans. Therefore, it's difficult to know how intermittent fasting will affect us similarly.

And while these studies suggest that intermittent fasting might have some positive effects on brain health, there are also potential drawbacks.

For example, in rats with Alzheimer's disease-induced estrogen deficiency, an intermittent fasting routine exacerbated bone mineral density loss and insulin resistance at fasting. So, as with any diet or lifestyle change, it's important to weigh the potential benefits against the potential risks.

Science can't say whether there are definitive intermittent fasting benefits for human brain health. More research is needed to draw any firm conclusions.

Longevity

While some evidence suggests that an intermittent fasting routine may have certain benefits, such as weight loss and improved insulin sensitivity, there is still much debate surrounding its long-term effects on human longevity.

I won't sugar-coat this here: many of the articles trying to claim this point to some pretty shitty science.

I did manage to come across a few decent-quality studies, but they didn't have the flashy results the intermittent fasting influencers want you to believe they do.

A 2019 study looked at time-restricted feeding (TRF) and its effect on markers related to longevity, such as blood glucose, autophagy, and oxidative stress. Overweight adults followed an early TRF schedule for four days, only eating between 8 am and 2 pm, then switched to a regular TRF schedule of 8 am to 8 pm for another four days.

The study found eTRF improved glycemic control by reducing glucose and insulin levels compared to the control schedule. This is significant because blood glucose levels are important for overall health and longevity. In fact, research has shown that fasting glucose levels can even predict longevity.

However, suppose we are talking about blood glucose levels again. In that case, we need to refer back to where we were discussing insulin sensitivity and the question: was it the meal timing, or was it the reduced calories responsible for the improved glycemic control?

Similarly, studies on laboratory rats and mice have shown that intermittent fasting and periodic fasting can improve many health indicators and counteract disease processes related to age-related disorders.

However, it's important to remember that what works in animals doesn't necessarily translate to humans. We need more randomized controlled clinical trials to establish the efficacy of intermittent fasting in improving general health and preventing major diseases of aging in humans.

The most these studies can say is that intermittent fasting MAY help with improving certain measures of health (such as blood glucose levels, chronic disease prevention, and reduced body fat) and that improving your health in that way MAY improve your longevity.

What we do know is that healthful eating patterns, regular exercise, and stress management are key components of a healthy lifestyle and long-term health. Therefore, prioritizing those health behaviors is probably more important instead of micro-managing your meal timing.

The Health Risks with Intermittent Fasting

Intermittent fasting is generally considered to be safe if done in moderation. However, there are some health risks associated with intermittent fasting that you should be aware of before giving it a try.

Low Blood Sugar

A common side effect of intermittent fasting is low blood sugar. When you fast, your body’s natural blood sugar levels drop. This can cause symptoms such as shakiness, irritability, and fatigue. It is important to mind your blood sugar levels when you are fasting. Don't try to push through hunger. Eat something if you start to feel unwell.

Headaches

Headaches are another common side effect of intermittent fasting. When you fast, the same drop in blood sugar levels can lead to headaches. Additionally, dehydration can also cause headaches. If you experience headaches from fasting, it is important to drink plenty of fluids and consume foods high in electrolytes, such as bananas or sweet potatoes.

Muscle Loss

If you do not consume enough calories, especially from protein, while intermittent fasting, you may also experience muscle loss. Maintaining muscle mass is essential for long-term health outcomes, so it is important to make sure you are still getting enough lean protein and calories while intermittent fasting to prioritize this - even if you are trying to lose weight.

Worsen existing medical conditions

If you have a medical condition, such as diabetes, high blood pressure, or an inflammatory disease, intermittent fasting can make it worse. This is because fasting can cause blood sugar and blood pressure fluctuations. If you have concerns about whether intermittent fasting is safe for you, speak with your doctor before starting.

Disordered eating patterns

Binge eating is a common problem among those who practice intermittent fasting, as they may be so hungry when they break their fast that they overeat through compensatory eating behaviors.

Binge eating can lead to various health problems, such as obesity, type II diabetes, and heart disease. Additionally, it can negatively impact mental health, causing feelings of guilt and shame.

Additionally, intermittent fasting can trigger or exacerbate disordered eating patterns for some people. I do not recommend intermittent fasting if you have a history of disordered eating or if you are struggling with an eating disorder.

Anxiety and irritability

Fasting can cause anxiety and irritability due to the body's lack of food and nutrients. This is especially true if you are already prone to anxiety or other mental health disorders.

If you find intermittent fasting is causing distress, stopping and opting for a different weight loss strategy is best.

Fasting May Not Be Safe for Everyone

While intermittent fasting may be safe for some people, it may not be safe for everyone. If you are pregnant or breastfeeding, have a history of eating disorders, or have any other health concerns, it is important to talk to your doctor before starting any fasting diet.

Remember: your health, physically and psychologically, is more important than any diet. Make sure to take care of yourself first and foremost.

Is there Actual Science Behind Intermittent Fasting?

The short answer is: yes, there is actual science behind intermittent fasting. Research has found that intermittent fasting can positively affect health and weight loss measures, such as reducing insulin levels and improving glycemic control. In addition, animal studies suggest intermittent fasting may help counteract disease processes related to age-related disorders.

However, we still need randomized clinical trials in humans to determine whether intermittent fasting is truly effective for weight loss and long-term health.

Additionally, what is science-based is not always what is evidence-based. Your personal preferences and lifestyle should be taken into account when deciding what works best for you.

Ultimately, if intermittent fasting resonates with you and fits into your life, it is probably safe to try. Intermittent fasting may have some positive benefits. However, it should not take precedence over a healthy diet and lifestyle.

If you're still working on learning the nutrition basics and nailing down regular physical activity, focus on those first before trying anything more complicated. After all, none of the proposed benefits of intermittent fasting have proven to occur independently of healthy eating and exercise.

Final Thoughts on Intermittent Fasting: Is it a Good Way to Lose Weight?

Intermittent fasting can be a safe and effective tool for weight loss, but it is important to remember that it isn't the only way to lose weight.

Eating a healthful diet, maintaining a caloric deficit, and regularly engaging in physical activity are all equally important for weight loss. Additionally, remember to always mind your mental health when it comes to dieting.

Finding the meal timing that works best for your schedule is a part of maintaining a healthy lifestyle. Whether that includes fasting or not is up to you.

• References

  Anti-inflammatory mechanism of dieting and fasting revealed. (n.d.). ScienceDaily. Retrieved May 30, 2023, from https://www.sciencedaily.com/releases/2015/02/150216131146.htm

  Baik, S., Rajeev, V., Fann, D. Y., Jo, D., & Arumugam, T. V. (2019). Intermittent fasting increases adult hippocampal neurogenesis. Brain and Behavior, 10(1), e01444. https://doi.org/10.1002/brb3.1444

  Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: A review of human findings. Translational Research, 164(4), 302–311. https://doi.org/10.1016/j.trsl.2014.05.013

  Ezzati, A., Rosenkranz, S. K., Phelan, J., & Logan, C. (2023). The Effects of Isocaloric Intermittent Fasting vs Daily Caloric Restriction on Weight Loss and Metabolic Risk Factors for Noncommunicable Chronic Diseases: A Systematic Review of Randomized Controlled or Comparative Trials. Journal of the Academy of Nutrition and Dietetics, 123(2), 318-329.e1. https://doi.org/10.1016/j.jand.2022.09.013

  Heilbronn, L. K., & Ravussin, E. (2003). Calorie restriction and aging: Review of the literature and implications for studies in humans. The American Journal of Clinical Nutrition, 78(3), 361–369. https://doi.org/10.1093/ajcn/78.3.361

  How Intermittent Fasting Impacts Longevity: A Summary of the Research. (n.d.). Retrieved May 30, 2023, from https://blog.insidetracker.com/intermittent-fasting-impacts-longevity-summary-research

  Hutchison, A. T., Liu, B., Wood, R. E., Vincent, A. D., Thompson, C. H., O’Callaghan, N. J., Wittert, G. A., & Heilbronn, L. K. (2019). Effects of Intermittent Versus Continuous Energy Intakes on Insulin Sensitivity and Metabolic Risk in Women with Overweight. Obesity, 27(1), 50–58. https://doi.org/10.1002/oby.22345

  Jamshed, H., Beyl, R. A., Della Manna, D. L., Yang, E. S., Ravussin, E., & Peterson, C. M. (2019). Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients, 11(6), 1234. https://doi.org/10.3390/nu11061234

  Jordan, S., Tung, N., Casanova-Acebes, M., Chang, C., Cantoni, C., Zhang, D., Wirtz, T. H., Naik, S., Rose, S. A., Brocker, C. N., Gainullina, A., Hornburg, D., Horng, S., Maier, B. B., Cravedi, P., LeRoith, D., Gonzalez, F. J., Meissner, F., Ochando, J., … Merad, M. (2019). Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool. Cell, 178(5), 1102-1114.e17. https://doi.org/10.1016/j.cell.2019.07.050

  Lee, J., Duan, W., Long, J. M., Ingram, D. K., & Mattson, M. P. (2000). Dietary restriction increases the number of newly generated neural cells, and induces BDNF expression, in the dentate gyrus of rats. Journal of Molecular Neuroscience: MN, 15(2), 99–108. https://doi.org/10.1385/JMN:15:2:99

  Liu, D., Huang, Y., Huang, C., Yang, S., Wei, X., Zhang, P., Guo, D., Lin, J., Xu, B., Li, C., He, H., He, J., Liu, S., Shi, L., Xue, Y., & Zhang, H. (2022). Calorie Restriction with or without Time-Restricted Eating in Weight Loss. New England Journal of Medicine, 386(16), 1495–1504. https://doi.org/10.1056/NEJMoa2114833

  Mattson, M. P., Longo, V. D., & Harvie, M. (2017). Impact of intermittent fasting on health and disease processes. Ageing Research Reviews, 39, 46–58. https://doi.org/10.1016/j.arr.2016.10.005

  Roman, Y. M., Dominguez, M. C., Easow, T. M., Pasupuleti, V., White, C. M., & Hernandez, A. V. (2019). Effects of intermittent versus continuous dieting on weight and body composition in obese and overweight people: A systematic review and meta-analysis of randomized controlled trials. International Journal of Obesity, 43(10), Article 10. https://doi.org/10.1038/s41366-018-0204-0

  Shin, B. K., Kang, S., Kim, D. S., & Park, S. (2018). Intermittent fasting protects against the deterioration of cognitive function, energy metabolism and dyslipidemia in Alzheimer’s disease-induced estrogen deficient rats. Experimental Biology and Medicine (Maywood, N.J.), 243(4), 334–343. https://doi.org/10.1177/1535370217751610

  Sutton, E. F., Beyl, R., Early, K. S., Cefalu, W. T., Ravussin, E., & Peterson, C. M. (2018). Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism, 27(6), 1212-1221.e3. https://doi.org/10.1016/j.cmet.2018.04.010

  Youm, Y.-H., Nguyen, K. Y., Grant, R. W., Goldberg, E. L., Bodogai, M., Kim, D., D’Agostino, D., Planavsky, N., Lupfer, C., Kanneganti, T. D., Kang, S., Horvath, T. L., Fahmy, T. M., Crawford, P. A., Biragyn, A., Alnemri, E., & Dixit, V. D. (2015). The ketone metabolite β-hydroxybutyrate blocks NLRP3 inflammasome–mediated inflammatory disease. Nature Medicine, 21(3), Article 3. https://doi.org/10.1038/nm.3804

  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