Have you ever had a special event coming up, like a wedding, and wanted to lose weight quickly for the event? You might have cut way back on calories and ramped up your exercise, hoping to reach your target weight as fast as possible — but how successful were you?
Chances are you lost weight, at least initially. Then the weight loss slowed. In response, you cut back your calorie intake even more and exercised longer. When you stepped on the scale a week later, you were surprised to find your weight had changed very little. Plus, you felt tired and discouraged because you were eating too little and over-exercising.
The Consequences of Excessive Calorie Restriction
Under-eating and over-exercising is a vicious cycle to get into and one that can lead to malnutrition, exhaustion, fertility problems, bone loss, and eating disorders. Why is excessive calorie restriction and exercise so damaging to the body?
Each of us has a resting metabolic rate, the rate at which our body burns energy at rest, based on our unique genetics, age, body composition (the amount of muscle we carry) and whether we’re healthy — have a normal thyroid and are free of other diseases that can impact metabolic rate.
For the most part, your resting metabolic rate stays within a relatively narrow range, although your metabolism as a whole can be elevated after a high-intensity exercise session or, to a lesser degree, by eating a meal. Your body has to work harder to digest and absorb food, especially foods high in protein.
Stress can also affect your metabolism. When you’re anxious, you release hormones like adrenalin that transiently increases your metabolic rate, but longer term it seems to slow metabolism. A study carried out at Ohio State University showed women who reported stressful events the previous day burned 104 fewer calories than other women after eating a high-fat meal.
The Damaged Metabolism
So what is a “damaged metabolism?” Metabolic damage is where your resting metabolism slows as a result of doing too much of the wrong kind of exercise or because you’ve reduced your calorie intake too much. A damaged metabolism is often the result of an overzealous attempt to lose weight fast.
You’re probably already familiar with why your metabolism slows when you reduce your calorie intake too much. Your body is a fine-tuned machine that wants to maintain homeostasis, in particular: it needs a steady supply of energy to keep your body running. When it senses a deficiency in energy, it goes into conservation mode, only burning the minimum amount of energy your cells need for survival. It does this in a number of ways, most notably by slowing thyroid function. After all, your thyroid is the “master gland” when it comes to your metabolism.
You may have heard the body’s efforts to conserve referred to as “starvation mode.” Another term for this phenomenon is “adaptive thermogenesis,” the adaptations your body makes to help maintain a constant energy supply.
The other way people damage their metabolism is by doing long periods of moderate-intensity cardio, especially in conjunction with calorie restriction. Doing this creates an energy deficit that causes your metabolism to slow in response. Plus, calorie-restricted cardio also leads to muscle breakdown due to the effects of cortisol, the “stress hormone” released in response to stress, calorie restriction or exercise, which funnels the amino acids from protein breakdown to the liver. Once there, the amino acids can be converted to glucose by a process called gluconeogenesis. The goal of gluconeogenesis is to give your body more glucose to maintain your blood sugar level during times of stress.
Muscle breakdown to make glucose may be beneficial short term, but not so much longer term. Losing muscle mass causes further metabolic slowing. Yes, you may lose weight through restrictive dieting and long periods of cardio, but how much of that weight loss is fat and how much muscle? Eventually, this cycle leads to metabolic damage and increased stress on your body. If you’re in this type of cycle, you need to break it — but how?
Recovering from Metabolic Damage
It’s best to avoid damaging your metabolism in the first place by eating regular meals, consuming an appropriate number of calories for your activity level and not overdoing steady-state cardio. Of course, if you’re trying to lose weight, a calorie deficit works in your favor, but never reduce your calorie intake by more than 500 calories below your daily requirements. Otherwise, you’re getting into a range where your metabolism could slow. But what if you’ve already damaged your metabolism?
Fortunately, just as your metabolism slows when you underfeed it for long periods of time, you can jumpstart it again by again supplying your body with more macronutrients. The best way to do this is to slowly increase your calorie intake, making sure the calories you’re consuming are nutrient-rich, including lean sources of protein, fiber-rich carbohydrates, and healthy fats. By increasing your calorie intake slowly, you’ll give your metabolism a chance to gradually increase in response to better nutrition.
Increase the frequency of your meals by eating 5 or 6 small meals a day. This will ensure your body doesn’t go for long periods of time without fuel. Include a lean source of protein with every small meal and snack. Protein has the greatest “thermogenic” effect, meaning it increases your metabolic rate when you consume it more than carbohydrates or fats do.
What about Exercise?
Cut back on moderate-intensity cardio and the length of your workouts by doing some shorter, HIIT (high-intensity interval training) routines. Most importantly, devote more of your workout time to resistance training, with an emphasis on compound exercises, using resistance heavy enough to build lean body mass. If you’ve gone through a long period of under-nutrition, you’ve probably lost lean body mass and need to rebuild it to restore your metabolism to a more normal state. Muscle is more thermogenic than fat.
Will You Gain Weight as You Repair Your Metabolism?
You may gain a small amount of weight initially as you increase your calorie intake, but a portion of that weight gain will be water and glycogen. Chances are you’ve depleted your glycogen stores with aggressive exercise and dieting, and as you restore them your weight will increase.
If you still need to lose weight, once you’ve transitioned to a more reasonable diet and exercise plan, you can slowly reduce your calorie intake after two or three months to no more than 500 calories under maintenance to help restart the weight loss process. Don’t do this until you’ve maintained a diet with the appropriate number of calories and macronutrients for a month or two and you’re feeling healthy and energetic again. Most importantly, don’t let your metabolism get damaged again by being too aggressive with your diet and exercise plan.
Am J Clin Nutr October 2008 vol. 88 no. 4 906-912
Ohio State University. “Weighty Issue: Stress and High-Fat Meals Combine to Slow Metabolism in Women”
J Am Coll Nutr. 2004 Oct;23(5):373-85.
Nutrition & Metabolism 2004, 1:5 doi:10.1186/1743-7075-1-5.
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