Slow metabolism? The biggest diet myth explained scientifically

Identifying a bad diet is much easier than finding a good one. For example, “only eat this” diets are generally bad. Diets that only let you eat one food or are very restrictive with what you are allowed to eat can lead to nutrient deficiencies. In addition to the three macronutrients— carbohydrates, proteins, and fats—there is a multitude of micronutrients—vitamins, minerals, trace elements—that our bodies need regularly to maintain body and organ functions. A long-term deficiency can have dramatic effects, from sleep disorders to depression to osteoporosis and cardiovascular diseases. ¹ Instead of stimulating your metabolism, they will harm it in the long term. So we have a first answer to the initial question: can a diet damage my metabolism? The answer is: yes—if the diet creates a nutrient deficiency.

Always avoid such diets. An unbalanced diet is never healthy and recovery from malnutrition is slow and requires much effort. Long-term nutrient deficiency can cause permanent damage. Therefore, always pay attention to your health, activity level, and sense of well-being while you are on a diet. If you notice that one of these three areas begins to decline— e.g. you are constantly getting sick, feeling drained, underperforming or in a permanently bad mood—you should take a break from this diet. But that doesn’t mean that you should binge on desserts, chips or other junk food, but rather nourish yourself with healthy, whole foods.

There is a lot of talk about boosting metabolism, but what does that actually mean? Basically, this is a very general phrase. The term “metabolism” refers to all of the body’s chemical processes to process certain nutrients. When someone says they have a good metabolism, they are often referring to their ability to maintain or lose weight easily. Metabolic processes take place at all times. While genetics are an important factor, the right foods also play a decisive role in how fast your metabolism is.

Many diets do not put you at risk of nutrient deficiency because they are less restrictive to your food choices. How do they work and do they also pose a danger to your metabolism? Although diets differ in details, most of them involve creating a calorie deficit and thus rely on simple math: They give your body fewer calories than it currently needs so that it gets the missing calories from your body’s reserves. In the best case, your body gets these reserves from its subcutaneous fat stores, because the ultimate goal of any diet for weight loss is to reduce body fat—mostly with a focus on the stomach and legs. Sounds simple and logical: I simply give my body less energy (calories) and it breaks down its fat deposits.

A little trick to boost your motivation to move (and thus fight your inner couch potato) is to listen to motivating music before working out or to watch short sport or fitness videos related to the workout that you are about to do. Regular exercise is the best way to improve your general motivation to move (tonic dopamine level in the striatum) and thus helps to increase your overall daily activity level. Take advantage of every opportunity to move that comes up, even if it’s just a flight of stairs that you sprint up with gusto because you’re feeling the urge to do so. So if you reduce calories to lose weight, make sure you motivate yourself to exercise enough, because your body will try to lower your activity level. This effect can be countered in the short term by increasing your calorie intake.

So how do you boost your metabolism? You’re going to get the most results in this area with the right diet and an active lifestyle. You can easily calculate how many calories you should be eating to reach your goal with our calorie calculator.

Not only your activity level but also your body composition and health can suffer from an insufficient amount of calories. A diet without sufficient amounts of protein—just like a diet without exercise—will cause your body to lose muscle mass.⁶ To ensure that your body is supplied with all the nutrients it needs (particularly even when you create a calorie deficit )make sure you are eating a balanced, wholesome diet.

Why so? Let us take a look at the basic diet model from above: The body gets fewer calories than it needs and gets the missing energy (because food is ultimately energy plus building materials) from the body’s own stores. Your body, however, adjusts quickly to the new conditions: it adapts to the lack of calories by burning less energy. In the short term, as described above, your movement behavior is adjusted via your neurotransmitters. Without realizing it, you start moving less and burning fewer calories, and your motivation to move also begins to suffer from the calorie restriction.

The second victim of this strategy is our fatless body tissues (including skeletal muscles). Overall, your fat-free body mass is the largest energy consumer (i.e. calorie burner) in your body and is an essential factor for energy consumption at rest – the largest proportion of the calories you burn every day. However, unlike your organs, the nervous system, and the brain, this energy consumer is absolutely unnecessary for our body. If you do not exercise during a diet, your body will lose some muscle mass with every pound that you lose. ⁷ Less muscle mass means that you burn fewer calories and thus lose less weight. Muscles weigh more than fat. So your pant size will not decrease proportionally to the weight you lose. Conversely, there are many exercisers who build up considerable muscle mass through regular strength training and —despite ultimately weighing more on the scales— get a significantly slimmer, more athletic figure than before.

Both a regular strength training program and a protein-based diet will help protect your muscle mass, which is usually reduced when you lose weight. Not only will you look better by doing this, but it also is good for your posture and will also save you having to get fit again afterward finishing your diet phase. For every ten kilograms of weight loss, there are about three kilograms of pure muscle mass loss. With a proper fitness plan and a diet rich in protein, the proportion can be reduced to about one and a half kilograms.

Therefore, make sure to not only use the scale to gauge how much fat you have lost but also to get yourself some measuring tape – changes in body measurements are often more accurate for evaluating changes in your body size. We recommend that you step on the scale once a week and at the same time to measure your abdominal and chest circumference. These measurements provide you with an understanding of your physical changes that is much more realistic than the number on the scale could ever provide. To summarize: when dieting, you want to maintain your muscle mass and reduce your body fat, so make sure you get enough exercise and protein.

The terms “fast” and “slow” metabolism are often heard in conversation but not actually thoroughly researched. These terms came into being with the observation that people who lose weight very quickly (particularly formerly obese people) have a significantly reduced energy metabolism after the phase of intense weight loss. If you consider the above explanations, it quickly becomes clear that a reduced metabolism caused by rapid weight loss is normal: less voluntary and involuntary movement, less fat-free mass than energy consumers, less weight to be carried and less digestive work due to less food—all of this reduces our energy consumption. Lower energy metabolism due to weight loss is therefore quite normal so that the amount of food required after a diet to maintain weight will be less than before the diet. But that shouldn’t reduce your motivation. With adequate training and the right nutrition, you can activate your metabolism.

Should you be worried about all this with respect to your own diet? No—if you arm yourself with the proper knowledge and plan you have nothing to worry about. The “biggest losers”, like participants in other studies, had a massive calorie deficit of sometimes more than 1000 kcal per day, plus they practiced an average of three hours of exercise per day over a period of three hundred days, and competed with each other every week. As is so often the case in life: consistent, patient hard work brings you to your goal more successfully and healthier than quick-fixes and short-term thinking. Extreme diets with a high calorie deficit should only be used for a very short time and seem to be tolerated better by people with high muscle mass and rather low body fat. Better not to take such extreme measures at all. All you really need is motivation, plus perseverance and patience.