Intermittent Fasting and Weight Loss
By: Tedi Nikova, BASc, MPH ( c )
Intermittent fasting (IMF) has been popular in the media for weight loss, specifically a diet that restricts the time window where an individual can eat, often referred to as time restricted feeding (TRF). The most popular time block that is all the rage is a 16 hour fast, 8 hour eating window. The theory behind TRF is that the body has a chance to metabolize stored energy from the body in those 16 hours, as energy is not directed to metabolism, as well as the shorter eating window helps with calorie reduction, as there is less time to consume a greater number of calories. There are several approaches to intermediate fasting, however the main focus will be on the strategy of TRF in this article.
Weight Loss
There have been only a few research trials conducted exploring the 8-hour window, 16-hour fast that have lasted over 8 weeks, with none of the trials comparing TRF to basic calorie restriction. A 2019 systemic review reported that reducing the eating window an individual has for consuming food, resulted in modest weight loss compared to control group with no time restriction on food consumption. Additionally some studies showed significant reduction in body fat percentage, however there is a lack of long term studies, (Rynders, Thomas, Zaman, Pan, Catenacci, Melanson, 2019). TRF can aid in weight loss, by reducing the calories an individual consumes in their day, by simply having less time to consume food, (Ryenders et al, 2019). A 2017 meta-analysis comparing IMF to calorie energy restriction (CER), found that IMF and CER both reported a significant weight loss associated with improvements in metabolic outcomes, with no difference in weight loss between IMF and CER. (Harris, Mcgarty, Hutchison, Ells, Hankey, 2017). There is however limited research on comparing TRF to a calorie restricted diet, to better understand if TRF is impacting weight loss beyond a regular calorie restriction diet.
Limitations to these studies is a lack of long-term studies of IMF, as well as variable measurement methods for the adherence to TRF, as a large component of weight loss is the individuals ability to fit the dietary patterns into their everyday lives.
Metabolic Benefits
A 2019 meta- analysis found that the metabolic benefits from IMF included small reductions in total cholesterol, LDL cholesterol, triglycerides and fasting glucose and insulin, that is influenced by weight loss, rather than the TRF, as both CER and TRF had similar effects on metabolic markers, (Rynders, Thomas, Zaman, Pan, Catenacci, Melanson, 2019). In a 2017 systemic review, IMF caused larger reductions in body fat percentage compared to CER. IMF also caused Significant decreases in total cholesterol and LDL cholesterol, as well as reduction in BP and TG levels, greater than that of CER, (Harvie, Howell, 2017). There is however a lack of long-term studies on IMF, as well as specifically TRF, as this systemic review focuses on alternative day fasting of two day energy restriction and alternate day fasting, (Harvie et al, 2017). It is important to be aware that majority of the research that has been done on IMF, has been on healthy overweight men and women, therefore there needs to be more investigation if any metabolic benefits were attributed to the weight loss or independent of weight loss.
What It Comes Down To
My interpretation from the research that has been done so far, I will share three common themes I have identified for TRF:
1. TRF allows for larger meals, due to the shorter period of time an individual has time for in the day to consume food.
2. Less opportunity to over consume calories, as the eating window is restricted.
3. Due to the restricted time you have to eat, it becomes even that more important to choose high nutrient value fruits and vegetables, lean meats, plant proteins, healthy oils and whole grains.
Possible Negative Side Effects.
The TRF diet approach can interfere with social interactions. Having a limited amount of time to eat, can interact with social events, that require later or earlier feeding times. This can have an effect on family activities or celebrations, or simple a romantic dinner with your partner, which can in turn affect the quality of social relationships.
Having larger meals can contribute to bloating. Individuals that are more sensitive to bloating or suffer from gastrointestinal disorders such as IBS are not recommended to consume larger meals, but rather smaller more spaced out meals, (Cozma-Petruţ, Loghin, Miere, Dumitraşcu, 2017).This can become challenging when following TRF, as there is a limited time to consume food, and smaller portions may impact the opportunity for adequate calories and nutrients an individual has time to consume in a day.
References
Cozma-Petruţ, A., Loghin, F., Miere, D., & Dumitraşcu, D. L. (2017). Diet in irritable bowel syndrome: What to recommend, not what to forbid to patients! World Journal of Gastroenterology, 23(21), 3771. doi: 10.3748/wjg.v23.i21.3771
Harris, L., Mcgarty, A., Hutchison, L., Ells, L., & Hankey, C. (2017). Short-term intermittent energy restriction interventions for weight management: a systematic review and meta-analysis. Obesity Reviews, 19(1), 1–13. doi: 10.1111/obr.12593
Harvie, M., & Howell, A. (2017). Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects — A Narrative Review of Human and Animal Evidence. Behavioral Sciences, 7(4), 4. doi: 10.3390/bs7010004
Rynders, C. A., Thomas, E. A., Zaman, A., Pan, Z., Catenacci, V. A., & Melanson, E. L. (2019). Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients, 11(10), 2442. doi: 10.3390/nu11102442
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