Does Intermittent Fasting Work?

Intermittent fasting is a very popular diet trend, but does it work? In reality, it depends on how you do it.

                                    Everything you need to know about Intermittent Fasting

Article contributed by Nicole Rubin, Dietetic Intern

Intermittent fasting is a popular diet trend that is often credited with weight loss and metabolic health benefits. Let’s start by defining what constitutes intermittent fasting.

Intermittent fasting is an eating pattern in which a person cycles between periods of eating and fasting (1). There are different methods of practicing intermittent fasting.

Does Intermittent Fasting Work?

What is Intermittent Fasting?

Here are the most common methods:

• 16:8 intermittent fasting– fast for 16-hours and eat during an 8-hour window (1). This is also referred to as time-restricted eating.
• Alternate day fasting– fast for 24-hours a day, twice a week (1).
• 5:2 intermittent fasting – consume a very small amount of calories, essentially a fast, on two, non-consecutive days of the week and eat normally on the remaining five days (1). Typically 25% of your daily calories which works out to an average of 500 calories for women and 600 for men.

Following any of the intermittent fasting methods typically results in weight loss. A 2020 review on intermittent fasting and weight loss looked at 27 trials, and found that intermittent fasting resulted in weight loss of 0.8-13% from baseline (2). A 2017 JAMA Internal Medicine trial concluded that intermittent fasting is just as effective as daily calorie restriction for weight loss (3).

Time-restricted eating (the 16:8 method) is the most common schedule for intermittent fasting, so it’s what we are going to focus on for the reminder of the article. Time-restricted feeding dictates an eating window of 8-hours a day, but it doesn’t specify in which 8-hour window a person should be consuming their daily calories. Most people who practice this method of intermittent fasting skip breakfast and each lunch and dinner, usually between 12pm-8pm.

What does the research say about Intermittent Fasting?

A 2020 randomized clinical trial studied the effects of time-restricted eating on weight loss in men and women with overweight and obesity (4). In the study, the intervention group restricted eating between 12pm-8pm. The results from this study showed a significant decrease in weight in the time restricted eating group, but no significant change in the control group. Additionally, the difference between the two groups was not significant. This means that time restricted eating was actually not found to be more effective in weight loss, compared to the control group in this study who ate throughout the day. This study used the eating window of 12pm-8pm, and therefore participants were skipping breakfast.

Should I skip breakfast with intermittent fasting?

Is skipping breakfast OK with Intermittent Fasting?

Therefore, we have to ask the question, is skipping breakfast really the most effective way to practice intermittent fasting? We’ve all heard that breakfast is “the most important meal of the day” so why do so many people skip breakfast with the goal of weight loss and health benefits?   In order to understand why skipping breakfast may actually be counterintuitive for weight loss, let’s first look at the importance of eating breakfast.

Studies show that consuming a high protein breakfast is linked with increased muscle mass, energy expenditure, satiety hormones, and glucose regulation, all of which help with weight loss (5)(6). Eating breakfast, especially one that is full of protein, is associated with increased feelings of fullness and lower levels of ghrelin (7). Ghrelin is referred to as the “hunger hormone” because it stimulates hunger and leads to increased food intake.  Therefore, it may actually be more beneficial to have the 8-hour eating window earlier in the day.

What is circadian rhythm with intermittent fasting?

What is Circadian Rhythm?

Eating earlier in the day more closely aligns with the circadian rhythm. The circadian rhythm is a natural, 24-hour cycle that is part of our “internal clock” and regulates the sleep-wake cycle, hormone release, hunger cues, and other metabolic processes (8). It helps to regulate our energy expenditure, appetite, and insulin sensitivity (8). Our bodies were designed to go through a natural eat-fast cycle over the course of 24-hours; when we are awake (eat) vs. asleep (fast).

With the advances in technology, we no longer have to align our dietary habits with the natural sleep/wake cycle, and this often has negative consequences to our health. Since the circadian rhythm regulates enzymes and hormones involved in metabolic processes, a disruption in this can lead to obesity and insulin resistance (7).

Many of our metabolic processes peak early the day, and therefore eating in sync with the circadian rhythm can promote weight loss and improve various aspects of our metabolic health (8). Therefore, meal timing has implications in weight, appetite, satiety, and glucose and lipid metabolism (9). Studies have shown that those who eat later in the day and skip breakfast are actually at a greater risk for obesity and have increased lipogenesis compared to people who eat the same amount of calories earlier in the day (9).

Does Intermittent Fasting Work?

Does the timing of the eating window matter?

According to a 2019 randomized controlled trial, coordinating meal times with the circadian rhythms may be a powerful tool to reduce appetite, lose weight, and improve metabolic health (8). Eating earlier in the day may help to reduce hunger throughout the day, ultimately leading to weight loss (8). Participants in this study were overweight, but otherwise generally healthy. They were assigned to two different time restricted feeding schedules:

• A control, in which participants consumed three meals over a 12-hour period (8am-8pm)
• An early time restricted feeding schedule, in which participants consumed three meals over a 6-hour period (8am-2pm).

Early time-restricted feeding shifts the majority of caloric intake to earlier in the day. Results of this study showed that early time-restricted feeding helped to improve participants’ ability to switch from burning carbohydrates for energy to burning fat for energy (8). The results showed that early time-restricted feeding resulted in lower levels of ghrelin, the “hunger hormone,” and increased fat burned over a 24-hour period (8). This study found that early time-restricted feeding reduced ghrelin levels and increased feelings of fullness over the course of the day.  

Another study compared weight loss among overweight women who consumed a high-caloric breakfast vs. those who consumed a high-caloric dinner (7).

• Intervention group: breakfast was 700 calories, lunch was 500 calories, and dinner was 200 calories
• Control group: the distribution was opposite with 200 calories at breakfast, 500 calories at lunch, and 700 calories at dinner)

The high-calorie breakfast group had greater weight loss and a greater decrease in fasting glucose and insulin (7). Average triglyceride levels decreased by over 15% more in the high calorie breakfast group (7). The study also reports that consuming protein early in the day with breakfast, as opposed to at lunch or dinner, leads to increased satiety, and reduced concentrations of ghrelin, resulting in sustained weight loss (9). 

Does Intermittent Fasting Work? Key Takeaways:

Overall, the various methods of intermittent fasting can be seen as an effective weight loss strategy due to a reduction in overall caloric intake and a suppression in hunger. Though there is nothing “magic” about IF, and a caloric deficit is still required for weight loss.

More specifically, it’s important to look at when you are consuming the majority of your daily calories, rather than to just look for a reduction in daily caloric intake.

Aligning meals with the circadian rhythm by fueling your body earlier in the day may have additional benefits. It’s important to note that in order to see these benefits of consuming breakfast, one must choose to eat a high-protein breakfast, rather than one high in sugar and refined carbohydrates.

Further research is warranted to better understand the metabolic benefits of early time-restricted feeding in areas including blood lipid profiles and blood glucose control (10)(11). Research is currently being conducted to evaluate the impacts of meal timing on cardiovascular disease prevention, cancer prevention, and diabetes management (12)(13)(14).

***Each person is an individual and there are medical reasons that time restricted eating may not be a good idea for you, especially those with ANY history of disordered eating. Always discuss any type of diet plan with a doctor or registered dietitian, especially if you have any preexisting medical conditions.

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References:

1. Intermittent Fasting 101 — The Ultimate Beginner’s Guide [Internet]. Healthline. 2020 [cited 2020 Oct 22]. Available from: https://www.healthline.com/nutrition/intermittent-fasting-guide
2. Welton S, Minty R, O’Driscoll T, Willms H, Poirier D, Madden S, Kelly L. Intermittent fasting and weight loss: Systematic review. Can Fam Physician. 2020;66:117–25.
3. Time-restricted eating is growing in popularity, but is it healthy? [Internet]. www.heart.org. [cited 2020 Oct 22]. Available from: https://www.heart.org/en/news/2019/03/22/time-restricted-eating-is-growing-in-popularity-but-is-it-healthy
4. Lowe DA, Wu N, Rohdin-Bibby L, Moore AH, Kelly N, Liu YE, Philip E, Vittinghoff E, Heymsfield SB, Olgin JE, et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Intern Med [Internet]. 2020 [cited 2020 Oct 25]; Available from: https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2771095
5. Chanet A, Verlaan S, Salles J, Giraudet C, Patrac V, Pidou V, Pouyet C, Hafnaoui N, Blot A, Cano N, et al. Supplementing Breakfast with a Vitamin D and Leucine–Enriched Whey Protein Medical Nutrition Drink Enhances Postprandial Muscle Protein Synthesis and Muscle Mass in Healthy Older Men. J Nutr. Oxford Academic; 2017;147:2262–71.
6. Meng H, Matthan NR, Ausman LM, Lichtenstein AH. Effect of prior meal macronutrient composition on postprandial glycemic responses and glycemic index and glycemic load value determinations. Am J Clin Nutr. Oxford Academic; 2017;106:1246–56.
7. Abrams L. Study: Eat Protein in the Morning [Internet]. The Atlantic. 2013 [cited 2020 Oct 25]. Available from: https://www.theatlantic.com/health/archive/2013/03/study-eat-protein-in-the-morning/274417/
8. Ravussin E, Beyl RA, Poggiogalle E, Hsia DS, Peterson CM. Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans. Obesity. 2019;27:1244–54.
9. Jakubowicz D, Barnea M, Wainstein J, Froy O. High Caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women. Obesity. 2013;21:2504–12.
10. Santos HO, Macedo RCO. Impact of intermittent fasting on the lipid profile: Assessment associated with diet and weight loss. Clin Nutr ESPEN. 2018;24:14–21.
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12. St-Onge Marie-Pierre, Ard Jamy, Baskin Monica L., Chiuve Stephanie E., Johnson Heather M., Kris-Etherton Penny, Varady Krista. Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement From the American Heart Association. Circulation. American Heart Association; 2017;135:e96–121.
13. Antunes F, Erustes AG, Costa AJ, Nascimento AC, Bincoletto C, Ureshino RP, Pereira GJS, Smaili SS. Autophagy and intermittent fasting: the connection for cancer therapy? Clinics (Sao Paulo). 2018;73:e814s.
14. Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11.