Does Weight Loss Really Just Come Down to Calories In vs. Calories Out?

I am sure you have heard it one time or another, in order to lose weight (or gain weight) all that matters is calories in versus calories out.

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Basically, in order to lose weight, someone simply needs to eat less and/or exercise more, right? Right!

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Calories in and calories out does matter. There's a reason people are put on low calorie diets prior to bariatric surgery - fast weight loss. Don't believe it? Try and fast for 2 weeks, you’ll lose weight! Your body has baseline caloric needs and if those calories aren't supplied by food, they'll be primarily supplied by body fat - which in turn, equals weight loss. *Note: Please don't actually try fasting for weight loss -- it rarely works*

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However, while calories in vs. calories out does matter and it is technically right and it sounds simple for weight loss, please realize, it is not as easy as some make it out to be.

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A professor I work with who specializes in exercise metabolism is known for always saying:

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“Weight balance is simple, but that does not mean it's easy”

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I think this statement beautifully sums up the weight loss process. Essentially, we know the overall goal (i.e., consume less and expend more), yet on a regular basis - it can be much more difficult than it sounds.

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So, if you are reading this and know anything about me, you probably think I am going to highlight various physiological factors that highlight this point. Factors such as HPA axis activation and how it ultimately impacts weight loss (Figure 1) or how extreme exercise and energy expenditure actually causes reductions in sleep energy expenditure in order to preserve energy – ultimately slowing down weight loss (Figure 2).

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However, I don't plan to do this as the underlying physiology is only ONE piece of the ever changing and confusing puzzle that is weight loss. The reason physiology can’t be the only focus with weight loss is because even though we can (pretty much) control exactly how much we eat and move, we ABSOLUTELY cannot always control and change our environment and/or behaviors (at least not quickly). So although our body works to regulate and maintain homeostasis (i.e., calorie balance), it is regularly affected by and responds to environmental and behavioral stimuli (Figure 3).

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Impacting Weight Balance (3).

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For example, we live in an environment with an abundance of processed and easily digestible foods increasing our likelihood to overeat. Then when we do overeat, homeostatic controls essentially attempt to increase our weight set-point to a slightly higher weight to prevent further weight gain. However, we tend to keep overeating and so this process keeps happening - resulting in more weight gain. Another example that impacts weight balance are behavioral factors. If you are regularly getting less than 7 hours of sleep per night, stress stays high, cognitive control declines, we are more prone to overeat, choose higher calorie options, are more hungry, etc. So again, these factors might not directly cause weight loss but they indirectly have a very large impact.

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That said, if you are trying to lose weight and not focusing on calorie consumption, you are doing it wrong. However, if you are only worried about calories and not monitoring other behavioral and environmental factors, you are also doing it wrong.

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Whether directly or indirectly, physiology, psychology, and environment impact us all the time! So when it comes to weight loss, calories in vs. calories out does matter but it for sure shouldn't be the only factor you focus on!

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REFERENCES

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‍Hirotsu, C., Tufik, S., & Andersen, M. L. (2015). Interactions between sleep, stress, and metabolism: From physiological to pathological conditions. Sleep Science, 8(3), 143-152.

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Broskey, N. T., Martin, C. K., Burton, J. H., Church, T. S., Ravussin, E., & Redman, L. M. (2021). Effect of Aerobic Exercise-induced Weight Loss on the Components of Daily Energy Expenditure. Medicine and Science in Sports and Exercise, 53(10), 2164-2172.

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MacLean, P. S., Bergouignan, A., Cornier, M. A., & Jackman, M. R. (2011). Biology's response to dieting: the impetus for weight regain. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.

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