The impact of nutrition and exercise on weight loss

Table of contents:

How nutrition affects weight loss

Cutting calories to lose weight

The role of protein in fat loss  

Nutrition versus exercise: who wins?

When it comes to weight loss, does diet or exercise matter more?

Weight loss ultimately boils down to a calorie deficit: you must consume fewer calories than you burn.

You can theoretically create that deficit by eating less, burning more, or a combination of the two.

However, in practice, using exercise to drive weight loss pans out differently than changing your diet. Slogging away on a treadmill and cutting your calories aren’t equally effective. But that isn’t to say that both don’t have value in supporting sustainable fat loss.

In this article, you’ll learn about nutrition and exercise's impact on weight loss - and how to use each best to optimize your physique.

How nutrition affects weight loss

Nutrition plays a pivotal role in weight loss: cutting calories is a surefire way to lose weight. And strategically choosing where your calories come from can make sticking to your diet easier and more sustainable.

Cutting calories to lose weight

Reducing your calorie intake is the most straightforward approach to weight loss: if you simply eat fewer calories than you burn, you’ll lose weight.

There isn’t a “magic” diet required to see results. In fact, research finds that any diet that limits your food intake to create a calorie deficit will enable weight loss - given you actually adhere to it(1). With adherence being the key component. If you only stick to a diet sporadically, you’ll never create the consistent calorie deficit necessary to lose weight. And when it comes to dietary adherence, calories aren’t the full story. Rather, your specific food choices can make all the difference in making a diet both sustainable and enjoyable.

The role of protein in fat loss  

In particular, eating a diet high in protein will yield better results and adherence than a diet low in protein, since protein helps you…

1. Preserve muscle while dieting

Typically, a weight loss goal aims to lose fat, not muscle - and getting sufficient protein can facilitate such fat loss(2). Eat ~1 gram of protein per pound of lean body mass to promote muscle preservation during a calorie deficit.

2. Support satiety

Protein is more satiating compared to carbohydrates and fats, which can help stave off hunger when you’re cutting calories(3). Accordingly, research finds that following a high-protein diet can naturally help individuals regulate their calorie intake - so they lose weight(4, 5) and keep it off(6).

3. Modestly boost your metabolism

Protein not only helps reduce calorie intake but also slightly increases your calorie expenditure due to its high thermic effect of feeding (TEF). TEF refers to the energy your body expends digesting a macronutrient - and protein beats carbs and fats by far, since your body uses ~20-30% of your calories from protein during digestion(7)! So, for example, if you consume 200 calories of protein in a meal, you’ll burn off 40 to 60 of those calories with TEF! And while 40 calories might seem small, the calories add up after many meals and days.

4. Getting fiber for satiety & sustainability

Alongside protein, fiber also contributes to dietary adherence. More specifically, fiber promotes sustainable weight loss(8) by…

  1. Supporting satiety: Fiber enhances satiety by slowing digestion and expanding in the digestive tract. Moreover, high-fiber foods often require more chewing, which buys time for your brain to register satiety before you reach for seconds.
  1. Curbing hunger and cravings by stabilizing blood sugar: Large spikes and dips in blood sugar can spur hunger and cravings. Fortunately, fiber slows the rate at which glucose enters your bloodstream, keeping your blood sugar stable and cravings in check.

  1. Allowing you to eat more with fewer calories: Many high-fiber foods are less calorie dense, so you can eat more volume without exceeding your calorie budget.

How exercise affects weight loss

The role of exercise in weight loss is slightly more nuanced. Although exercise has numerous health benefits and can help you maximize your metabolism, it generally burns fewer calories than most people realize. That said, research on weight loss interventions find that combining exercise with diet supports greater and longer-term weight loss than diet alone(9, 10, 11).  

Maximizing your metabolism

Physical activity is one of the only means by which we can increase our daily energy expenditure. But it’s important to have realistic expectations about how much exercise can boost your metabolism: one hour of moderate-intensity cardio burns only ~300-400 calories, which you could easily eat back in a small snack.

Moreover, many people mistakenly add back the calories they think they’ve burned from exercise - so they end up eating more, which eliminates the deficit they’d worked so hard to create!

Over time, cardio tends to burn even fewer calories than you’d expect due to various adaptations, such as…

  • Greater movement efficiency - The more you practice a particular movement, the more efficient your mechanics become and the less energy you need to perform that exercise(12).
  • Reduction in body mass - As you lose weight, you’ll expend less energy during exercise since you’re lighter (i.e., have less mass to move).
  • Reduction in non-exercise-activity thermogenesis (NEAT) - When you ramp up exercise to create a calorie deficit, your body tends to compensate by reducing your non-exercise activity(13).
  • Enhanced metabolic efficiency during a calorie deficit - Simply being in a calorie deficit induces metabolic changes that reduce calorie burn during exercise(14).

Consequently, if you’re turning to cardio to burn calories, use it sparingly and strategically - preferably when you’re in a weight loss plateau or struggling to keep your calories sufficiently low. And when you do incorporate cardio, you should...

  1. Start conservatively
  2. Control your calorie intake
  3. Keep your expectations realistic
Enhancing appetite regulation & dietary adherence

Although some people may use exercise as a license to eat more, research actually finds that properly programmed exercise may enhance satiety signals, leading to better appetite regulation(15, 16). Furthermore, regular exercise can strengthen self-regulation, so you’re more likely to make healthy food choices and stick to your diet(17).

Resistance training to preserve muscle

Lastly when it comes to exercise, resistance training will likely enhance fat loss more than cardio(18). While cardio might burn more calories acutely, within your workout window, resistance training can increase your metabolism when you aren’t working out.

And if you really want to maximize fat loss and your metabolism, resistance training will help ensure you preserve muscle - so you lose more fat and less muscle during your diet. Since muscle is more metabolically expensive than fat tissue, maintaining muscle can keep your metabolism and calorie intake higher to support sustainable weight loss.

Nutrition versus exercise: who wins?

All things considered, diet drives weight loss more than exercise.

Focusing on cardio to lose weight leads to limited progress and diminishing returns: you simply can’t out-exercise a poor diet(19). The amount of time and effort required to burn sufficient calories from exercise alone is both unrealistic and unsustainable. But that doesn’t mean that exercise is useless.

Cardio has a time and place. When used wisely, it can break a weight loss plateau while helping you keep the weight off long-term. Meanwhile, resistance training plays a crucial role in muscle preservation, to both optimize fat loss and enhance your metabolism.

So stop using exercise to burn fat. When it comes to weight loss, cutting calories is key. Adding exercise is optimal but ultimately optional.

  1. Alhassan, S., Kim, S., Bersamin, A., King, A. C., & Gardner, C. D. (2008). Dietary adherence and weight loss success among overweight women: results from the A TO Z weight loss study. International journal of obesity, 32(6), 985-991.
  2. Haghighat, N., Ashtary-Larky, D., Bagheri, R., Mahmoodi, M., Rajaei, M., Alipour, M., ... & Wong, A. (2020). The effect of 12 weeks of euenergetic high-protein diet in regulating appetite and body composition of women with normal-weight obesity: a randomised controlled trial. British journal of nutrition, 124(10), 1044-1051.
  3. Westerterp-Plantenga M. S. (2003). The significance of protein in food intake and body weight regulation. Current opinion in clinical nutrition and metabolic care, 6(6), 635–638.
  4. Weigle, D. S., Breen, P. A., Matthys, C. C., Callahan, H. S., Meeuws, K. E., Burden, V. R., & Purnell, J. Q. (2005). A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. The American journal of clinical nutrition, 82(1), 41-48.
  5. Skov, A. R., Toubro, S., Rønn, B., Holm, L., & Astrup, A. (1999). Randomized trial on protein vs carbohydrate in ad libitum fat reduced diet for the treatment of obesity. International journal of obesity, 23(5), 528-536.
  6. Claessens, M., Van Baak, M. A., Monsheimer, S., & Saris, W. H. M. (2009). The effect of a low-fat, high-protein or high-carbohydrate ad libitum diet on weight loss maintenance and metabolic risk factors. International journal of obesity, 33(3), 296-304.
  7. Tappy L. (1996). Thermic effect of food and sympathetic nervous system activity in humans. Reproduction, nutrition, development, 36(4), 391–397.
  8. Howarth, N. C., Saltzman, E., & Roberts, S. B. (2001). Dietary fiber and weight regulation. Nutrition reviews, 59(5), 129-139.
  9. Curioni, C. C., & Lourenco, P. M. (2005). Long-term weight loss after diet and exercise: a systematic review. International journal of obesity, 29(10), 1168-1174.
  10. Miller, W. C., Koceja, D. M., & Hamilton, E. J. (1997). A meta-analysis of the past 25 years of weight loss research using diet, exercise or diet plus exercise intervention. International journal of obesity, 21(10), 941-947.
  11. Look AHEAD Research Group (2014). Eight-year weight losses with an intensive lifestyle intervention: the look AHEAD study. Obesity (Silver Spring, Md.), 22(1), 5–13.
  12. Barnes, K. R., & Kilding, A. E. (2015). Running economy: measurement, norms, and determining factors. Sports medicine - open, 1(1), 8.
  13. King, N. A., Caudwell, P., Hopkins, M., Byrne, N. M., Colley, R., Hills, A. P., Stubbs, J. R., & Blundell, J. E. (2007). Metabolic and behavioral compensatory responses to exercise interventions: barriers to weight loss. Obesity (Silver Spring, Md.), 15(6), 1373–1383.
  14. Rosenbaum, M., Vandenborne, K., Goldsmith, R., Simoneau, J. A., Heymsfield, S., Joanisse, D. R., Hirsch, J., Murphy, E., Matthews, D., Segal, K. R., & Leibel, R. L. (2003). Effects of experimental weight perturbation on skeletal muscle work efficiency in human subjects. American journal of physiology. Regulatory, integrative and comparative physiology, 285(1), R183–R192.
  15. Martins, C., Morgan, L. M., Bloom, S. R., & Robertson, M. D. (2007). Effects of exercise on gut peptides, energy intake and appetite. Journal of Endocrinology, 193(2), 251-258.
  16. Beaulieu, K., Hopkins, M., Blundell, J., & Finlayson, G. (2018). Homeostatic and non-homeostatic appetite control along the spectrum of physical activity levels: An updated perspective. Physiology & behavior, 192, 23–29.
  17. Joseph, R. J., Alonso-Alonso, M., Bond, D. S., Pascual-Leone, A., & Blackburn, G. L. (2011). The neurocognitive connection between physical activity and eating behaviour. Obesity reviews : an official journal of the International Association for the Study of Obesity, 12(10), 800–812.
  18. Clark, J. E. (2015). Diet, exercise or diet with exercise: comparing the effectiveness of treatment options for weight-loss and changes in fitness for adults (18–65 years old) who are overfat, or obese; systematic review and meta-analysis. Journal of Diabetes & Metabolic Disorders, 14(1), 1-28
  19. Thorogood, A., Mottillo, S., Shimony, A., Filion, K. B., Joseph, L., Genest, J., ... & Eisenberg, M. J. (2011). Isolated aerobic exercise and weight loss: a systematic review and meta-analysis of randomized controlled trials. The American journal of medicine, 124(8), 747-755.

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