Intermittent Fasting: Is it better than your typical weight loss diet?


  • green onion, red chili peppers, lemon slice, fork, knife and alarm clock

With diet trends constantly emerging and changing, it can be hard to keep up! The amount of information available on the internet can also make it difficult to figure out which trends are worth attempting. While we can't possibly seek to explore every fad diet, let's talk about one diet approach that had recently been gaining popularity: intermittent fasting. Specifically, we'll explore how it compares to the standard weight loss diet. But first, let's start with the basics.

What is intermittent fasting?

Intermittent fasting is a form of dieting that restricts when to eat rather than what to eat. There are a few different methods for intermittent fasting. The essential component of each method is that you have periods of eating and periods of not eating, called fasting. During fasting periods, you are allowed to drink water, tea, and black coffee, but you are encouraged not to eat or drink anything that contains calories.

  • Alternate day fasting, the 5:2 method, and time-restricted eating are the main methods of intermittent fasting.
  • Alternate day fasting1 is when you alternate fasting days, where calories are restricted to 500 for women and 600 calories for men, with “feast” days, where you can eat whatever you want. For reference, 500 calories is about equal to one bagel with cream cheese.
  • The 5:2 method1 of intermittent fasting is when you eat your normal diet with no restrictions 5 days of the week, but fast on 2 non-consecutive days.
  • Time-Restricted Eating is perhaps the most popular form of intermittent fasting, and likely the one you have heard the most about. Time-restricted eating involves limiting when you can eat within a 24-hour period2. The goal is to only eat for 8-12 hours during the day, for example, only eating from 11 am until 7 pm. This idea of time-restricted eating is that the timing of when we eat can affect body weight, blood sugar, heart health, and our overall health3

So, let’s dive into what the evidence says about how intermittent fasting compares to a standard weight loss diet in terms of effects on body weight, blood sugar, and heart health.

Intermittent fasting and weight loss

The standard method recommended for weight loss is known as continuous energy restriction. In simple terms, this just means limiting the number of calories you eat and drink every day of the week. Since many people struggle to maintain this regimen, alternate methods are often sought to achieve weight loss, and intermittent fasting is one of them. Studies show that the 5:2 method, alternate day fasting, and time-restricted eating are all just as effective for weight loss as continuous energy restriction2,4. However, most studies only followed their participants for up to one year, so whether individuals who use intermittent fasting can maintain their weight loss long-term is not yet well known.

Takeaway: Intermittent fasting is just as effective for weight loss as continuous energy restriction, but whether it is a sustainable lifestyle for long-term weight loss is not well known.

Intermittent fasting and blood sugar

Intermittent fasting is often advertised as a diet approach than can help lower and/or maintain a healthy blood sugar level. Any beneficial effects of the 5:2 and alternate day fasting methods on blood sugar are probably a side effect of the weight loss they cause4,5. But what about with time-restricted eating? Is there a unique benefit to blood sugar levels when you control which hours you eat? While multiple studies have shown that time-restricted eating can lower blood sugar levels6, the evidence is conflicting, as other studies have found no benefits of time-restricted eating on blood sugar compared to continuous energy restriction6,8. Essentially, the evidence is not strong or clear enough to definitively say that intermittent fasting or, more specifically, time-restricted eating is more beneficial for blood sugar compared to continuous energy restriction.

Takeaway: We do not know if intermittent fasting improves blood sugar significantly in comparison to continuous energy restriction.

Intermittent fasting and heart health

Intermittent fasting can improve heart health in a similar manner to continuous energy restriction. Research has shown that intermittent fasting and continuous energy restriction can improve cholesterol levels and lead to decreased blood pressure, both of which are beneficial for heart health6,9. The evidence suggests that both lifestyles are similarly effective in inducing heart health benefits4.

Takeaway: Intermittent fasting and continuous energy restriction lifestyles both have heart health benefits.

Conclusion

Overall, the evidence shows us that, much like continuous energy restriction, intermittent fasting can lead to significant weight loss which provides a variety of health benefits including decreased blood sugar and improved heart health. There are some groups of people who may want to avoid intermittent fasting entirely or talk to a registered dietitian before attempting10:

  • Individuals under 18 years of age
  • Those with a history of eating disorders/disordered eating habits
  • Pregnant or breastfeeding individuals
  • Individuals with diabetes

While more research needs to be done to assess the long-term effects of intermittent fasting, if you may benefit from weight loss and intermittent fasting fits your lifestyle better than the typical continuous energy restriction diet, consider giving it a try!

References

  1. Harris L, Hamilton S, Azevedo LB, et al. Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database Syst Rev Implement Rep. 2018;16(2):507-547. doi:10.11124/JBISRIR-2016-003248
  2. Moon S, Kang J, Kim SH, et al. Beneficial Effects of Time-Restricted Eating on Metabolic Diseases: A Systemic Review and Meta-Analysis. Nutrients. 2020;12(5):1267. doi:10.3390/nu12051267
  3. Chaix A, Manoogian ENC, Melkani GC, Panda S. Time-Restricted Eating to Prevent and Manage Chronic Metabolic Diseases. Annu Rev Nutr. 2019;39:291-315. doi:10.1146/annurev-nutr-082018-124320
  4. Cioffi I, Evangelista A, Ponzo V, et al. Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. J Transl Med. 2018;16(1):371. doi:10.1186/s12967-018-1748-4
  5. Seimon RV, Roekenes JA, Zibellini J, et al. Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials. Mol Cell Endocrinol. 2015;418 Pt 2:153-172. doi:10.1016/j.mce.2015.09.014
  6. Moon S, Kang J, Kim SH, et al. Beneficial Effects of Time-Restricted Eating on Metabolic Diseases: A Systemic Review and Meta-Analysis. Nutrients. 2020;12(5):1267. doi:10.3390/nu12051267
  7. Allaf M, Elghazaly H, Mohamed OG, et al. Intermittent fasting for the prevention of cardiovascular disease. Cochrane Database Syst Rev. 2021;2021(1):CD013496. doi:10.1002/14651858.CD013496.pub2
  8. Gabel K, Hoddy KK, Haggerty N, et al. Effects of 8-hour time restricted feeding on body weight and metabolic disease risk factors in obese adults: A pilot study. Nutr Healthy Aging. 4(4):345-353. doi:10.3233/NHA-170036
  9. Meng H, Zhu L, Kord-Varkaneh H, O Santos H, Tinsley GM, Fu P. Effects of intermittent fasting and energy-restricted diets on lipid profile: A systematic review and meta-analysis. Nutr Burbank Los Angel Cty Calif. 2020;77:110801. doi:10.1016/j.nut.2020.110801
  10. Intermittent Fasting: What is it, and how does it work? | Johns Hopkins Medicine. Accessed February 27, 2022. https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermit…

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Author(s)

Julia Melius
UNH Extension Intern, Nutrition Connections