Intermittent Fasting vs. Frequent Meals: What Does the Science Say?

To eat (every 2-3 hours), or not to eat (at all, for hours)? That is the (huge) question. Fad diets can seem romantic, promising speedy results with the least amount of effort. But do they work, scientifically? Heather Huntsman, CSCS, Ph.D., explores two in particular: Intermittent Fasting and Frequent Meals. How does the science hold up in both of these trending eating patterns? 

For those of you who try to stay up-to-date on all the latest fitness and nutrition trends, an interesting shift has occurred in the last year away from eating several small meals throughout the day to a concept called “intermittent fasting.” Essentially, this means eating no or very few meals for set periods of time. While it’s no surprise that a new fad has taken over, the stark contrast between these two strategies should at least give a critically thinking person pause. So, what is the science behind these strategies? And is it possible that the science justifies both seemingly conflicting recommendations?

Before we explore the science, I want to first state that most popular diets do, in fact, have some nugget of scientific truth. If they didn’t, the diet, strategy, or recommendation wouldn’t work. My goal here is to clarify the underlying science behind these two contrasting strategies so you can make an informed decision and be intentional in your health decisions.

The Science Behind Frequent Meals

• The scientific principal behind this strategy is the thermic effect of food (TEF) also known as diet induced thermogenesis (DIT).¹
• The total number of calories that your body burns in a day is broadly categorized into approximately 60% resting or basal metabolic rate (the baseline energy that your body needs to stay alive), 30% activity, and 10% TEF.^2,3
• TEF accounts for the increase in metabolism that is a direct result of the energy needed to digest the food consumed.
• In theory, the more frequently you eat, the more frequently your metabolism gets that little increase.³
• The major word of caution with this strategy is that the more often you eat, the more total calories you are likely to consume throughout the day. So, the key is to consume very small meals with a strong consideration for macronutrient composition to ensure you don’t overshoot caloric need.

The Science Behind Intermittent Fasting

• The scientific principle behind this strategy is two-fold. First, the less time or days you eat, the less you eat (pretty simple, right!?). Secondly, in a fasted state, the body is able to switch from primarily burning carbohydrates to breaking down and burning fat stores.⁴
• When food intake is limited, it forces the body to tap into its fat stores for energy. The body then has potential to not only lose weight, but lose fat instead of muscle.⁴
• There are several different strategies to execute a fasting protocol, such as eating on alternate days, or time-restricted eating (such as the 16-hour fast and 8-hour feeding method within a 24-hour cycle), but there are not enough scientific studies to say which might have more benefit.^4,5
• That said, at this point, the data suggest that compared to constant energy restriction in traditional diets, intermittent fasting (assuming you keep your fasting times in the right range) can be muscle-sparring.⁵
• In my opinion, a major word of caution with this strategy is the major psychological component food restriction: there are social implications to not eating when others are and refusing to eat for long periods of time might be a slippery slope for some.

So, the short answer is that yes there is some scientific justification for both strategies. What’s important to keep in mind is that no matter what strategy you use to lose or maintain a healthy weight, your ability to stick with a plan over time is the key factor in its effectiveness. Both of the strategies described above have the potential to “work,” but you have to be intentional and plan ahead – and it certainly doesn’t hurt to understand why they work.

References:

1. Quatela A, et al. (2016) The Energy Content and Composition of Meals Consumed after an Overnight Fast and Their Effects on Diet Induced Thermogenesis: A Systematic Review, Meta-Analysis and Meta-Regressions. Nutrients 8(11) 670. doi: 10.3390/nu8110670.
2. Calcagno, et al. (2019) The Thermic Effect of Food: A Review. Journal of the American College of Nutrition 38(6):547-551. doi: 10.1080/07315724.2018.1552544.
3. Reed GW, et al. (1996) Measuring the Thermic Effect of Food. American Journal of Clinical Nutrition 63(2):164-169. doi: 10.1093/ajcn/63.2.164.
4. Anton SD, et al. (2018) Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting. Obesity 26(2): 254-268. doi: 10.1002/oby.22065
5. Rynders CA, et al. (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.