I’m a huge skeptic of diets, but I just read an article that seemed to indicate that the intermittent fasting diet can actually help lose weight. Now, the diet is not magical, it doesn’t make calories suddenly disappear, but it seems to work by a mechanism that causes a calorie deficit.
Now weight loss is a simple equation — calories burned must be greater than calories consumed. Humans are, in effect, a closed system — we don’t create calories from sunlight like plants, and we don’t absorb calories from the air. And we burn calories by doing anything from typing a long blog article to hiking up a mountain. There are no magical ways to change this calculation, despite the claims of many health nuts.
We are going to take a look at what is an intermittent fasting diet and this new research paper. Maybe some of you have tried it and it worked (or failed), then tell me in the comments that I’m either right or wrong.
What is the intermittent fasting diet?
Intermittent fasting, also known as intermittent energy restriction, is any meal timing schedule that cycle between voluntary fasting (or reduced calorie intake) and non-fasting over a given period. Methods of intermittent fasting include alternate-day fasting, periodic fasting, and daily time-restricted feeding.
One of the more common types of intermittent fasting diet is 16 hours of fasting followed by eight hours of food. No, that doesn’t mean you can consume extra food during the eight hours of food consumption, it just means that you consume your regular meals during a restricted period of time.
A systematic review of energy restriction diets showed that intermittent fasting diets had similar weight loss to continuous diets but with a slight improvement in metabolic syndrome and insulin levels.
A 2019 review concluded that an intermittent fasting diet may help with obesity, insulin resistance, dyslipidemia, hypertension, and inflammation.
The biological mechanism underlying this type of diet is complex, but preliminary research seems to support the following four stages:
- The fed stage, or absorptive stage, during satiety, when the primary fuel source is glucose and body fat storage is active, lasts about four hours.
- The postabsorptive stage, which lasts for up to 18 hours, is when glucagon is secreted and the body uses liver glucose stores as a fuel source.
- The fasted stage, which occurs after 12-36 hours of continued fasting, is when the body transitions progressively to other fuel reserves, such as fat, lactic acid, and alanine.
- The metabolic switch stage is when the body switches from preferential lipid synthesis and fat storage to the mobilization of fat to be metabolized into fatty acid-derived ketones to provide energy.
A 2019 review of diets, including alternate day fasting, time-restricted feeding, exercise, and overeating, found that body weight homeostasis, which is controlled by the brain, could not precisely correct “energetic errors” – the loss or gain of calories – in the short term. Thus, the intermittent fasting diet could temporarily disrupt homeostasis so that individuals would mobilize more fat for energy.
Now, this all sounds very scientific, but I need to warn you that it is very preliminary research. And this does not mean there is magical burning of calories — the basic principle that calories in must be less than calories burned is still observed. The difference is how the body responds to temporary fasting, which appears to force the body to use fat for energy during fasting periods, which may “burn” more calories.
In a paper published on 1 September 2022 in JAMA Internal Medicine, Courtney Peterson, Ph.D., of the University of Alabama at Birmingham, and colleagues reported on a randomized clinical weight-loss trial involving 90 adults with obesity over 14 weeks. They compared a group that used time-restricted eating (all caloric intake was restricted to eight hours — from 0700 to 1500) to a group where all caloric intake occurred over 12 hours). Each group consumed the same number of calories.
Here are the key results:
- The intermittent fasting diet group lost an additional 2.3 kg (5.1 lb) compared to the group that consumed the same number.
- The time-restricted energy-restricted group saw an average drop of 6.3 kg (13.9 lb), while those who underwent energy restriction alone saw a weight loss of 4.0 kg (8.8 lb).
- The time-restricted group had slightly more body fat loss (-1.4 kg/-3.1 lb), but it wasn’t statistically more significant than with the calorie-restricted diet alone.
- However, in a secondary analysis of the 59 participants who finished the 14-week trial, the time restriction diet did prove to be more effective for shedding body fat, -1.8 kg (-4.0 lb) and trunk fat, -1.2kg (-2.6 lb). I’m not a fan of secondary analyses, since there is a chance of confirmation bias in selecting a subgroup of participants.
Skeptical Raptor Rating™
I’m going to give this study a 3 out of 5 stars. Some of my issues are that the study population is small, with n=45 in each group. I’m used to clinical trials with 1500-2000 in each group. Such a small study population could lead to some unintentional bias and statistical weakness.
However, for just 14 weeks, this study showed that the intermittent fasting group did have a statistically significant larger loss of weight than the energy-restricted group which could eat whenever they wanted. A 2.3 kg greater weight loss does make me take notice.
I’m also concerned about the proposed biochemical mechanisms behind the observed weight loss. There is a lot of speculation without a lot of firm research that supports the mechanism.
The search for the next great diet fad is like hunting for a unicorn — we all want to see one, but we’re pretty sure it is just a fantasy. These studies seem to support intermittent fasting, but this old feathered dinosaur wants to see some more data before jumping on board.
- Anton SD, Moehl K, Donahoo WT, Marosi K, Lee SA, Mainous AG 3rd, Leeuwenburgh C, Mattson MP. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018 Feb;26(2):254-268. doi: 10.1002/oby.22065. Epub 2017 Oct 31. PMID: 29086496; PMCID: PMC5783752.
- Cahill GF Jr. Fuel metabolism in starvation. Annu Rev Nutr. 2006;26:1-22. doi: 10.1146/annurev.nutr.26.061505.111258. PMID: 16848698.
- Cioffi I, Evangelista A, Ponzo V, Ciccone G, Soldati L, Santarpia L, Contaldo F, Pasanisi F, Ghigo E, Bo S. 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 Dec 24;16(1):371. doi: 10.1186/s12967-018-1748-4. PMID: 30583725; PMCID: PMC6304782.
- de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2019 Dec 26;381(26):2541-2551. doi: 10.1056/NEJMra1905136. Erratum in: N Engl J Med. 2020 Jan 16;382(3):298. Erratum in: N Engl J Med. 2020 Mar 5;382(10):978. PMID: 31881139.
- Jamshed H, Steger FL, Bryan DR, Richman JS, Warriner AH, Hanick CJ, Martin CK, Salvy SJ, Peterson CM. Effectiveness of Early Time-Restricted Eating for Weight Loss, Fat Loss, and Cardiometabolic Health in Adults With Obesity: A Randomized Clinical Trial. JAMA Intern Med. 2022 Sep 1;182(9):953-962. doi: 10.1001/jamainternmed.2022.3050. PMID: 35939311; PMCID: PMC9361187.
- Levitsky DA, Sewall A, Zhong Y, Barre L, Shoen S, Agaronnik N, LeClair JL, Zhuo W, Pacanowski C. Quantifying the imprecision of energy intake of humans to compensate for imposed energetic errors: A challenge to the physiological control of human food intake. Appetite. 2019 Feb 1;133:337-343. doi: 10.1016/j.appet.2018.11.017. Epub 2018 Nov 23. PMID: 30476522.
- Monnier L, Colette C, Lapinski H, Boniface H. Self-monitoring of blood glucose in diabetic patients: from the least common denominator to the greatest common multiple. Diabetes Metab. 2004 Apr;30(2):113-9. doi: 10.1016/s1262-3636(07)70097-6. PMID: 15223983.
- St-Onge MP, Ard J, Baskin ML, Chiuve SE, Johnson HM, Kris-Etherton P, Varady K; American Heart Association Obesity Committee of the Council on Lifestyle and Cardiometabolic Health; Council on Cardiovascular Disease in the Young; Council on Clinical Cardiology; and Stroke Council. Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement From the American Heart Association. Circulation. 2017 Feb 28;135(9):e96-e121. doi: 10.1161/CIR.0000000000000476. Epub 2017 Jan 30. PMID: 28137935; PMCID: PMC8532518.