Your weight loss progress is going well until one week goes by, then several, and there are no changes on the scale. It’s easy to assume: Has dieting damaged my metabolism? Not at all. According to doctors and scientists, it’s normal for your metabolic rate to slow down as you lose weight. But it doesn’t prevent you from losing more weight or cause weight to rebound.
Can metabolism damage flatline your weight loss? Photo by Diana Polekhina, Unsplash.
Metabolism “is not about calories per se, but how we utilise fuel, explains Dr Julinda Lee, a functional medicine doctor in private practice and our resident health advisor. This fuel comes from food (glucose) or fat from our reserves, for all the functions that the body needs to perform.
When people lament about a “damaged metabolism” in reference to how they are not losing weight, not losing it fast enough, or hitting a plateau, they are moaning about an “inefficient” metabolic rate.
Unlike metabolism which remains fairly constant throughout our adult lives until our 60s, our metabolic rate is not static. It’s also different for different individuals.
Our metabolic rate, as Dr Lee clarifies, “specifically refers to the utilisation of calories, that is the burning of energy in a given unit of time (whether per hour or day).”
Calories are a measure of energy, and for a sedentary adult, this is how calories are utilised:
• Basal metabolic rate (BMR) is the energy you burn for simply existing. Just to keep the heart, brain, and cells working uses up 50 to 70 per cent of our calories.
• Dietary thermogenesis, also known as the thermic effect of food (TEF) takes up a small percentage – 10 to 15 per cent.
• Physical activity – this includes both exercise and non-exercise activities like walking, taking the stairs, or fidgeting. It takes up 20 to 30 per cent of our calories.
Together, they account for your total daily energy expenditure (TDEE).
What affects metabolic rate?
Age and genetics can affect your metabolic rate, but body size and composition have a more direct influence on how high or low your metabolic rate is.
Big bodies need more energy to move and burn more calories during exercise than smaller ones. Hence a heavier person has a higher BMR than a lighter one. But if you’re sedentary and consuming more calories than needed, it makes it hard to get rid of body fat.
Individuals who have more lean muscle mass also have a higher BMR since muscles are more metabolically active than fat. Therefore, even when doing nothing, women will burn fewer calories than men, because they carry less muscle. Similarly, as people get older and tend to lose muscle and gain fat, this impacts their BMR.
Dieting or fasting (both can help you lose weight) also affects BMR.
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Dr Spencer Knaldosky, an obesity and lipid specialist in the US, shares: “Your resting or basal metabolism will decrease as you lose weight. This is normal. It’s because you have less mass. Whether it’s just fat or a mix of muscle and fat, your metabolism will decrease.”
A smaller you needs less energy (fewer calories) to function and that accounts for the adjustment. You’re not broken.
Refocus your efforts
Every person who loses an amount of weight will experience some metabolic slowdown. It’s meant to occur. Building more muscle can offset the changes in your BMR by some, but instead of obsessing over your metabolic rate, it’s more effective to focus on things you can change, advises Menno Henselmans, an exercise and nutrition scientist.
Weight or more accurately fat loss boils down to creating an energy gap: To get smaller, you need to expend more calories than you consume. Similarly, to maintain weight, energy balance matters.
The “fundamental problem for most people, in the long run, is appetite. And that has to be proportional to energy expenditure,” says Henselmans.
Dr Knaldosky concurs. “When people stop losing weight it’s because their perceived effort is high, but they are no longer in a caloric deficit (not burning more calories than they are eating). It’s the eating part and less non-exercise activity that makes the biggest difference though not the resting metabolic change.”
Just as your BMR changes when you shrink, your calorie budget gets affected. Smaller bodies don’t need as much food. The calorie budget that gave you a deficit to lose weight, in the beginning, is now the calories needed to maintain your smaller body – hence no differential means no more weight loss.
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While the principle of energy balance does not change, work on how you can better achieve that calorie deficit. Dr Knaldosky says: “Eating fewer calories than you burn can be done in many ways.”
Instead of eating sensibly – and this can often result in overestimating your portions since it is not quantifiable – try food logging and tracking calories. His other suggestion: Choosing nutrient-dense foods over calorie-dense ones, so you fill up on less. Or you can reduce certain types of foods or macronutrients over others for example going keto or low-fat.
The challenge is real
Many things can stall your progress of shedding weight, especially when there is a significant amount of it to lose. Understanding why they happen will give you a better idea of how to mitigate these temporary hiccups and not let them derail you.
Recalibrating your nutrition can help with satiety issues to manage hunger better. Photo by Clark Douglas, Unsplash.
• Your hunger goes into overdrive
When you calorie cut to lose body fat, Dr Lee says this can rev up your hunger responses. As body fat decreases, you also produce less leptin. Leptin is our satiety hormone and helps to suppress appetite. On the other hand, ghrelin our hunger hormone increases, which drives us to eat. This hormonal interplay is in place to regulate our body’s energy balance. Think of them as signallers to prevent us from starving and overeating, from a survival standpoint. But it can make it more challenging when you’re trying to lose weight.
Most dieters will also exercise to speed up weight loss. “You may find yourself hungrier because the body produces more ghrelin to increase consumption. However, the increase in calorie consumption (due to exercise), may exceed the calories burnt during exercise,” she says.
Fortunately, there are ways to help with satiety issues, so you don’t overeat. Filling up on water stretches the stomach and tricks the brain into thinking it’s full. However, this might mean more bathroom visits. Not always convenient. Far more elegant is rethinking your nutrition to improve satiety. For example, opting for low-calorie but volume-dense foods. Think high-fibre, and more plant-based options that are also heart healthy. Or eating adequate protein and increasing healthy fat intake.
• You’re not burning as many calories from exercising
Exercise helps utilise more calories. But it’s easy to misjudge how many calories are burnt even if you use fitness trackers. These trackers may be better at monitoring heart rates but are less effective in determining calories burned during exercise. One study in 2019 looked at three top-selling fitness trackers and had its test participants walk on a treadmill for ten minutes at 4km per hour, followed by a 10-minute jog at 8km per hour. It was reported that there was as much as a 40.1 per cent variance in how many calories were expended through activity.
Our bodies are also adaptive. Over time, some of your workouts may not give the same calorie expenditure because the body gets more efficient at them. As you get lighter, it takes less energy to perform these exercises (less resistance weight). Unless you’re actively increasing the intensity, difficulty, duration, and frequency of your exercises, you’re not going to elicit as much burn as before.
Strength training is still the best for fat loss because there is no cap on energy expenditure and you build muscle mass which also keeps your BMR up. Photo by Jonathan Borba, Pexels.
Prioritising strength training is more advantageous for fat loss, says Henselmans. According to him, strength training, as defined by researchers, is “progressive resistance training, that is exercising against certain resistance and trying to increase that resistance”.
He shares that studies show that energy expenditure is constrained at very high levels of activity with the exception of high-intensity exercise, especially strength training. “Strength training is better for fat loss than cardio, per minute of time,”; and comparatively, strength training beats cardio or a combination of the two (meaning cardio and strength training).
There is no constraint to energy expenditure with strength training and you also build muscle mass which further increases your metabolic rate. It also suppresses appetite, which can help in lowering energy intake.
Cardio, he explains, caps out at high activity levels. Once that energy threshold is crossed you do not get more burn from increasing your step count. It does not help to decrease appetite, and “does next to nothing to build muscle beyond a novice level of physique,” he says.
He offers that strength training will help you get stronger and keep your metabolic rate up. The progressive overload will help you have a higher work output, that is higher energy expenditure.
• Your evolutionary mechanism kicks in
Dr Lee says your body can go into conservation mode, especially when one starts to have fewer fat cells, coupled with reduced calorie intake. To keep its homeostatic energy balance (read burn fewer calories), the body starts to downregulate some of its biochemical processes, prioritising necessary mechanisms for survival over elective ones.
You may feel sluggish because your body wills you to conserve energy, and it’s not unusual for people to move less and want to veg out when they get thinner.
Heat generation is another elective process that gets sacrificed. When you couple this with loss of dietary thermogenesis from eating less food or fewer meals, you do feel colder. And also less inclined to move.
Make a conscious effort to stay physically active. Dr Lee’s tip: Heat is generated from muscle contractions when you exercise. Being active also boosts your metabolism and energy levels. This minimises dips in energy output.
Damaged my metabolism? No, but it has adapted
What fuels the metabolic damage myth? Metabolic adaptation can happen in some. Also known as adaptive thermogenesis, Henselmans explains it’s when there is a decrease in energy expenditure that is beyond what would have been predicted by changes in body composition and the decreased thermic effect of food.
This however remains one of the most controversial issues in the obesity field, because there hasn’t been enough clinical relevance to metabolic adaptation, in response to underfeeding and weight loss.
Dr Knadolsky notes the range of metabolic adaptations is from zero per cent to 15 to 20 per cent in most extreme cases. The more important takeaway: These adaptations do not predict weight regain.
If metabolic damage was present, it would be most evident in athletes who need to bulk and cut regularly to meet weight divisions for competition. But this is not the case. Photo by Alora Griffiths, Unsplash.
While adaptive thermogenesis is present in some individuals, Henselmans says the idea of permanent downregulation of energy expenditure after dieting, is not true. He cites the example of bodybuilders and physique athletes who must regularly cut and bulk to meet weight divisions for competitions. They should have damaged metabolisms if so, but there is no evidence of metabolic damage when their body composition reverts.
He contends that our body has adaptive metabolisms in place to preserve homeostasis, that energy expenditure decreases when body composition is altered, and there is an increase in appetite. These forces may drive you to regain some of the weight you lost, at least a little.
Metabolic adaptability also varies per individual; some have very adaptive metabolisms, while others have a more static one, he shares. He points out that if you have a very adaptive metabolism, it’s also more difficult to change your weight, and this works both ways.
The homeostasis forces (he stresses they aren’t anti-starvation mechanisms) that buffer against weight loss also work the other way in resisting weight gain. He explains they are not trying to prevent you from getting lean, but instead, help to defend against changes per se in both directions to help you maintain body composition.
Don’t blame it on the yo-yo diets
The hard truth: Chronic dieting does not damage metabolism. It doesn’t prevent you from losing weight nor cause weight rebound.
Henselmans says: “It’s not that the body is just miraculously putting the fat back on, without your control – it’s very predictable.”
Backsliding is the cause of weight regain. He says, “they go on a diet, they go off the diet, and they go back to the same lifestyle that got them fat in the first place.”
With our predictable metabolism, the cycle will continue as often as you repeat the yo-yo diets, instead of making sustainable lifestyle (nutrition coupled with more activity) changes, he warns. Creating that permanent energy gap – that difference between energy expenditure and energy intake gets you leaner, and you can stay leaner if you maintain that lifestyle.
A sustainable approach to nutrition: It needs to support your energy expenditure with the goal of optimising your health. Photo by Spencer Stone, Pexels.
Increasing energy expenditure is not without effort, he notes, but “the biggest challenge for most people is to learn to cope with a lower energy intake.”
Dr Lee agrees that some are likelier to regain the weight because there is no continuity once they hit their goal weight and they revert to old eating patterns.
She advises: “Adopting a diet mentality – drastic restrictions in calories or vilifying food and cutting them out unnecessarily – can be self-sabotaging and unsustainable, long-term. Instead take a broader, comprehensive view to nutrition where it needs to support your energy expenditure, with the goal of optimising your health.”
