Intermittent fasting and weight loss
Intermittent fasting and weight loss

Intermittent fasting (IF) has been popular in the media for weight loss, specifically IF that restricts the time window where an individual can eat. The most popular type of IF in the media has been Time Restricted Feeding (TRF), where an individual limits their ‘eating window’, the time period where food is allowed to be consumed. 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 IF, however the main focus of this article will be on TRF.

Weight loss

The main allure of TRF, is the potential for TRF to offer a weight loss benefit, greater than that of regular calorie restricted diet. A 2019 systemic review found that reducing the eating window an individual has for consuming food, resulted in a modest weight loss compared to a control group with no time restriction on food consumption, with both groups being in a calorie energy restriction (CER) (Rynders, et al, 2019). A 2020 meta-analysis further demonstrated that for participants that were metabolically unhealthy, following TRF showed a significant decrease in body weight; in the healthy participants TRF did not show a weight reduction, but still showed beneficial effects such as fat mass reduction (Moon et al, 2020). A cross-sectional study conducted on participants in the Mediterranean healthy Eating, Aging, and Lifestyles (MEAL) study, gathered a random sample of over almost 2000 adults (Currenti et al, 2021).

Overall, the study results demonstrated that adults that had an eating window of 8-10 hours were less likely to be obese or overweight, and less likely to have hypertension, compared to participants reporting an eating window greater than 10 hours (Currenti et al, 2021). The authors concluded that since the different time feeding intervals had similar calorie, and nutrient intakes, the difference in health outcomes for a time restricted feeding window was not cofounded by dietary factors (Currenti et al, 2021).

Limitations in the current research is a lack of long-term studies of TRF, as well as variable measurement methods for the adherence to TRF, as a large component of weight loss is the individual’s ability to fit the dietary patterns into their everyday lives. There is however limited research on comparing TRF to a calorie restricted diet, to better understand if TRF impacts weight loss, beyond a regular calorie restricted diet.

Metabolic benefits:

A 2019 meta- analysis found that the metabolic benefits from TRF included small reductions in total cholesterol, LDL cholesterol, triglycerides, fasting glucose, and insulin (Rynders et al, 2019). However, the authors concluded that this was mainly influenced by weight loss, rather than the TRF, as both CER and TRF group participants had similar effects on metabolic markers (Rynders et al, 2019). In a 2017 systemic review, IF caused larger reductions in body fat percentage compared to CER;

IF 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 et al, 2017). There is however a lack of long-term studies on IF, as well as specifically studies exploring TRF impact on metabolic health, as this systemic review focused exclusively on alternative day fasting, two-day energy restriction and alternate fasting day (Harvie et al, 2017).

It is important to be aware that majority of the research that has been done on IF, and TRF has been on healthy overweight men and women, therefore there needs to be further investigation if metabolic benefits from IF can be attributed to the weight loss, or the metabolic benefits were independent of weight loss, and were the result of IF.

TRF following the circadian biology:

A promising new field of research with regards to TRF, is restricting an individual’s feeding window based on circadian biology. Circadian biology is our internal circadian clock; our body is programed to best digest, and use energy as fuel during the day, and prepare to rest and repair at night, with a focus away from digesting food (Patterson et al, 2017).

From a metabolic standpoint, post-meal insulin and glucose responses to meals increase across the day and into the night; hus, meals consumed at night are associated with greater post meal rise in blood glucose (Patterson et al, 2017).

The current research on TRF based on circadian biology is still very limited to animal models, however this field of research is promising, and on the rise (Patterson et al, 2017).

What it comes down to:

My interpretation from the research that has been done so far:

  • TRF allows for larger meals, due to the shorter period of time an individual has time for in the day to consume food.
  • TRF offers less opportunity to over consume calories, as the eating window is restricted.

My concerns as a dietitian:

  • The TRF diet approach can 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.
  • 2. 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.
  • 3. Due to the restricted time to eat, there is a greater likelihood of not meeting all of your nutrient needs. It becomes even that more important to choose high nutrient value fruits and vegetables, lean meats, plant proteins, healthy oils, and whole grains

Currenti, W., Buscemi, S., Cincione, R. I., Cernigliaro, A., Godos, J., Grosso, G., & Galvano, F. (2021). Time-Restricted Feeding and Metabolic Outcomes in a Cohort of Italian Adults. Nutrients, 13(5), 1651. doi:10.3390/nu13051651
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
Greger. (2019). Time Restricted Eating Put to the Test. Retrieved from: 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
Moon, S., Kang, J., Kim, S. H., Chung, H. S., Kim, Y. J., Yu, J. M., Cho, S. T., Oh, C. M., & Kim, T. (2020). Beneficial Effects of Time-Restricted Eating on Metabolic Diseases: A Systemic Review and Meta-Analysis. Nutrients, 12(5), 1267.
Patterson, R. E., & Sears, D. D. (2017). Metabolic Effects of Intermittent Fasting. Annual review of nutrition, 37, 371–393.
Pellegrini, M., Cioffi, I., Evangelista, A., Ponzo, V., Goitre, I., Ciccone, G., Ghigo, E., & Bo, S. (2020). Effects of time-restricted feeding on body weight and metabolism. A systematic review and meta-analysis. Reviews in Endocrine & Metabolic Disorders, 21(1), 17–33.
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

Working Time
  • Mon-Fri 8:30 AM to 5:00 PM
    Sat Once or twice a month
    8:30 AM -3:30 PM
Contact Info

1- Hour Diet Consultation (Video Or Telephone) + Individualized Diet Plans For $150 CAD*