Beware the allure of products and diet systems offering faster fat burning results and “metabolism boosting” effects – there is no silver bullet.
Your metabolism isn’t broken and your near-term fat loss goals are achievable provided they are part of a longer-term strategy. Utilize time-tested practices to keep your metabolism humming that don’t require supplements or elimination of foods.
How metabolism slows during weight loss
Decrease in resting metabolic rate (RMR)
Your body expends energy to keep you alive and at your current body weight. The more you weigh, the more energy required to keep you alive.
During weight loss, you become a smaller human being. It’s logical that you will burn fewer calories to survive as a smaller human. Alterations in autonomic nervous system and neuroendocrine function (notably, downregulation of thyroid hormone) decrease energy expenditure by decreasing heart rate, blood pressure, and muscle ATP consumption.
Decrease in non-exercise activity
There may also be reductions in energy expenditure greater than what can be predicted from predicted by a loss of body mass. This is known as adaptive thermogenesis.
A main component of adaptive thermogenesis is decreased non-exercise activity. It could be less fidgeting and moving about, more time sitting, or walking a little less. This decreased activity is often imperceptible, but equates to fewer calories burned per day. On top of this total lower amount of movement, less energy is required during that movement because your body is lighter.
Further, feelings of hunger and reduction in satiety play into the issue with upregulation of appetite stimulating hormone (ghrelin) and downregulation of appetite suppressing hormone (leptin) during calorie restriction. The simultaneous decrease in RMR and general activity, combined with increased hunger and reduced satiation create an environment to regain weight, perhaps even exceeding previous highs.
The best way to “boost” metabolism is to increase calories to maintenance levels*
Slowing of metabolism due to adaptive thermogenesis is small if you’re following a reasonable diet strategy, and can be all but eliminated through periods at maintenance calories. This can be accomplished by:
- Diet Breaks. usually, 1-3 weeks at maintenance calories during a dieting phase). These diet breaks do appear to be psychologically beneficial, provide metabolic support through suppression of appetite, and may also help with motivation in the gym!
- Maintenance Phases. Weeks to months at maintenance calories after a set period of dieting.
Energy expenditure will increase with increased energy and support recovery from the physical and mental fatigue associated with dieting. It may also help with training motivation and getting more out of your workouts.
If energy restriction has been severe, or you have been chronically dieting it may require an extended period at maintenance calories. Giving yourself the grace of time, and focusing on a balanced and micronutrient-dense diet is critical. Increasing calories to maintenance levels should not mean a big change in the foods you’re eating, it just means a little bit more food, and a little bit more flexibility. Meeting your protein requirements and consuming veggies and fruits per day should continue to be the foundation.
*This is not to be confused with the clickbait phrase “eat more to lose weight”, which is in reference to transitioning from highly processed, high calorie density foods to lesser processed, less calorie dense foods resulting in reduce calorie intake for more food volume. What I’m referring to above is intentionally increasing calories (taking yourself out of energy deficit in a controlled way) for a period of time, so that your body in a good position to make the best progress during a subsequent diet phase.
Ignore marketing hype.
There’s no evidence pointing to a boosted metabolism using certain diet type. Outcomes for fat loss are similar comparing keto, low carb, and intermittent fasting to lower fat, higher carb diets (at the same calorie and protein levels). Terms heavily relied upon by ketogenic and low carb diet marketers are turning your body into a “fat burning machine” or “reprogramming” the body to use fat for fuel. Fat burning (oxidation of fatty acids for energy) is NOT the same thing as losing body fat.
Net energy dictates gain (calories in > calories out), maintenance (calories in ~ calories out), or loss of tissue (calories in < calories out)
- If you eat more calories from fat, you will burn more fat AND store more fat. If your diets is low in carbohydrates, your body will become more efficient at oxidizing fatty acids for energy (aka fat adaptation). This does NOT mean you will lose body fat! Net energy deficit dictates loss of fat.
- If you eat more carbs, you will expend more energy from carbs, store carbs in your muscles, and convert excess to fat. If your diet is higher carbohydrate, your body is more efficient at oxidizing carbohydrates for fuel.
Take home points
- Avoid extreme calorie restriction.
- Take fat loss in discrete phases, versus chronic dieting
- Form habits around maintaining daily activity (not related to exercise). For example, a 5-10 minute walk on a work break or in the evening after dinner. Identify pleasurable activities that you can stick with long after the dieting period is over.
- Hit your protein target within your calories because it 1) supports your lean mass and 2) has a slightly higher energy cost to absorb and digest, for a marginal addition to daily energy expenditure.
- Eat foods that satisfy you and make you feel great. The best healthy nutrition habits are the ones you can stick with.
I hope you found this helpful. Have any questions? Please contact me.
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Further reading:
Hall, K.D. Metabolic Adaptations to Weight Loss. Obesity 26, 5 (2018).
Nunes, C.L.; Casanova, N. et al., Does adaptive thermogenesis occur after weight loss in adults? A systematic review. Br J Nutr., 25, 1 (2021).
Garthe, I.; Raastad, T.; et al., Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. Int J Sport Nutr Exerc Metab., 21, 97 (2011).
Trexler, E.T., Smith-Ryan, A.E. & Norton, L.E., Metabolic adaptation to weight loss: implications for the athlete. J Int Soc Sports Nutr 11, 7 (2014).
Drummen, M.; Tischmann, L.; et al., High Compared with Moderate Protein Intake Reduces Adaptive Thermogenesis and Induces a Negative Energy Balance during Long-term Weight-Loss Maintenance in Participants with Prediabetes in the Postobese State: A PREVIEW Study. J Nutr., 150(3), 458 (2020).
Rosenbaum, M.; Leibel, R.L. Adaptive thermogenesis in humans. Int J Obes (Lond), 34 Suppl 1, S47 (2010).
Peos, J.J.;, Helms, E.R., et al., Continuous versus Intermittent Dieting for Fat Loss and Fat-Free Mass Retention in Resistance-trained Adults: The ICECAP Trial. Med Sci Sports Exerc. 53(8), 1685 (2021).
