When the scale won’t budge it’s easy to chalk it up to a slow metabolism. What about that guy who lives off doughnuts and never seems to gain a pound? He must have a fast metabolism, right? Well, not exactly. The answer is a little complicated, but the good news is that even if you struggle with your weight, there are things you can do to boost the amount of calories you burn.

Why It Matters

Metabolism is the set of chemical reactions that happen in our body to convert food into energy. This process helps to fuel all of the functions we need to live, from breathing to keeping our heart beating. Another way of thinking of metabolism is total daily energy expenditure (TDEE), which accounts for all the calories we burn in a day.

Lots of things can influence TDEE, like body composition (how much fat and muscle a person has), age, activity, and how much someone eats. The more muscle someone has, the more calories they require to maintain that muscle[1]. Younger people also tend to have higher metabolisms[2].

Based on these factors, everyone has a unique TDEE, and thus, a unique calorie requirement[3]. While our metabolisms are special snowflakes with their own individual energy needs, the number of calories we burn is still largely dependent on our diet and activity levels. In most cases, excess weight is due to eating too much and/or moving too little[4]. Slow metabolisms are rare and usually not the cause of obesity.

“I don’t really believe in ‘fast’ or ‘slow’ metabolism. It’s much more complicated than that,” says Krista Scott-Dixon, PhD, research director for the Healthy Food Bank and creator of women’s weightlifting site, stumptuous.com. “In fact, if your bodyweight is higher, you are just as likely to have a “fast” metabolism — because you probably have more lean body mass (including bone density) to carry a larger body around, and your body has to make a larger system function properly.”

You’re the Boss — The Answer/The debate

There are situations where hard work doesn’t pay off. When people have hormonal issues such as hypothyroidism or Cushing syndrome it’s much more difficult to lose weight. There are also certain genes that predispose folks to be overweight or obese.

Fortunately, thyroid disorders can be treated and genes only play small role in determining weight[5][6]. Ultimately, we do have control over our body size, even those who have a genetic predisposition to be heavy.

To lose weight, one must burn more calories than they take in, either through reducing the amount they eat, exercising more, or a combination of the two. It’s the good ol’ calories in vs. calories out model[7]. There are also certain methods that increase metabolism. But for the most part, eating healthy and being active are the best choices for staying trim[8].

Further Resources:  

  1. Metabolic Effect — Is Your Metabolism Broken?
  2. Time — Can Exercise Trump Genetics?
  3. Precision Nutrition — Genes vs. Workout Program
  4. Mayo Clinic: Metabolism And Weight-loss: How You Burn Calories
  5. Top 10 Foods That Boost Metabolism

Works Cited:
1. Factors influencing variation in basal metabolic rate including fat-free mass, fat mass, age, and circulating thyroxin but not sex, circulating leptin, or triiodothyronine. Johnstone, AM., Murison, SD., Duncan, JS., et al. Aberdeen Centre for Energy Regulation and Obesity, Aberdeen, Scotland, United Kingdom. The American Journal of Clinical Nutrition, 2005 Nov; 82(5):941-8.
2. Energy requirements and aging. Roberts, SB., Dallal, GE. Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts. Public Health Nutrition, 2005 Oct;8(7A):1028-36.
3. Human energy expenditure in affluent societies: an analysis of 574 doubly-labelled water measurements. Black, AE., Coward, WA., Cole, TJ., et al. Dunn Clinical Nutrition Centre, Cambridge, United Kingdom. European Journal of Clinical Nutrition, 1996 Feb;50(2):72-92.
4. Understanding and addressing the epidemic of obesity: An energy balance perspective. Hill, JO. Center for Human Nutrition, University of Colorado School of Medicine, Denver, Colorado. Endocrine Reviews, 2006 Dec;27(7):750-61.
5. Genetic determinants of obesity. Current issues (In German).  Hebebrand, J., Bammann, K., Hinney, A. Department of Child and Adolescent Psychiatry and Psychotherapy, University of Duisburg-Essen, Essen, Germany. Bundesgesundheitsblatt Gesundheitsforschung Gesundheitsschutz, 2010 July;53(7):674-80.
6. Polygenic obesity in humans. Hinney, A., Hebebrand J., Department of Child and Adolescent Psychiatry and Psychotherapy, University of Duisburg-Essen, Essen, Germany. Obesity Facts, 2008:1(1);35-42.
7. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. Sacks, FM., Bray, GA., Carey, VJ. Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts. The New England Journal of Medicine, 2009 Feb;360(9):859-73.
8. Who does not gain weight? Prevalence and predictors of weight maintenance in young women. Ball, K., Brown, W., Crawford, D. Centre for Physical Activity and Nutrition Research, Deakin University, Melbourne, Australia. International journal of obesity, 2002;26(12):1570-78.

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