Metabolic Adaptations & Considerations for a Weight-loss Diet

While you are in a calorie deficit, your body will have metabolic and compensatory adaptations to aid its survival — to preserve its fat stores in the face of food scarcity. Some individuals will have greater metabolic adaptations and/or subconscious compensatory behaviors in a negative energy balance than others, but everyone will have some degree of metabolic adaptation after a period of prolonged calorie restriction (typically seen after 4–12 weeks in >/= 500 net calorie/day deficit). That being said, there are many factors that also impact your daily calorie burn while in a calorie deficit.

1. As you reduce your calorie intake, you will reduce the amount of calories you burn to digest your food. Food has a thermic effect, since it takes energy (calories) to digest your food.
2. When you reduce your calorie intake and/or add in more cardiovascular activity, your body will try to compensate by reducing your daily NEAT (non-exercise activity thermogenesis, i.e., all movement during the day you would not categorize as exercise, such as fidgeting, walking to your car etc.) Your body will have greater compensations to an increase in activity, than it will to a reduction in calories. This is why restricting calories is a better idea in most cases than adding lots of cardio. When your calories get too low to continue restricting to create a deficit, cardio can be added to help with your compliance to your diet.
3. Your body will produce more cortisol to help raise your dropping blood sugars to account for a negative energy balance. This then can decrease your insulin sensitivity, reduce your sleep quality and/or duration, and suppress your thyroid hormone production (T3). Further, with less sleep a person will secrete more cortisol and ghrelin (hunger hormone) the following day, worsening this cycle. Over time, these elevations in cortisol will then disrupt your regular sex hormone production. In women, cortisol will increase androgen production. Conversely, cortisol will suppress a man’s testosterone production. These hormonal shifts all aim to preserve our fat stores will facing a famine…or a weight-loss diet.

Signs of a slowed metabolism:

1. A decrease in average body temperature and/or feeling colder than usual. Most people will feel warmer during or following a meal as a result of the thermic effect of feeding, but when their metabolism has slowed down significantly, they will feel cold even during a meal.
2. Lethargy: your drive to do daily tasks has decreased. A person may avoid tasks such as washing their car, getting their mail, running errands etc., to avoid exerting energy.
3. Your scale weight has plateaued or has started to increase while following a diet that was previously a calorie deficit.
4. You have fewer bowel movements and/or constipation. Please note: with less total food volume, this will happen to some degree regardless of a metabolic slow down and pre-existing gut conditions may contribute to this as well.
5. Your average resting heart rate has decreased even without the utilization of cardiovascular training.
6. Changes to your regular sleep patterns: interrupted sleep cycles, fewer total hours asleep, or sleeping longer than usual.

Strategies to counter these survival mechanisms:

1. When you run out of room to cut calories from your diet, you can increase the amount of protein you are eating with the same calories to create a larger energy deficit. Protein has a much larger thermic effect when compared to fats and carbohydrates; your body requires more energy (calories) to digest protein. Protein also increases your leptin sensitivity (satiation hormone) and it helps preserve your lean mass. Maintaining your muscle mass while dieting will help preserve your metabolic rate.
2. Use a fitness tracker to track your daily steps and maintain the same step count throughout the course of your diet to prevent your body’s drive to compensate for a negative energy balance by restricting your daily energy expenditure.
3. If you have been doing the same form of cardio, try switching up the type of cardio, and the intensity and duration. Once you become more efficient at one form of cardio, you burn fewer calories for the same work.
4. To promote better bowel motility, drink 2 tbsp of apple cider vinegar in the morning on an empty stomach and drink plenty of water. Vinegar stimulates the release of bile from your gall bladder, which acts as nature’s laxative and aids digestion. You may also want to supplement with a probiotic to promote a more balanced gut bacteria.
5. Avoid adding in a lot of cardio or reducing a large amount of food at the start of a diet. The idea is to make the least amount of changes to still lose an appropriate amount of weight each week. Your metabolism will adapt faster will adapt faster to more extreme changes than it will adapt to moderate changes. Dramatic shifts alarm your body and they will cause more dramatic hormonal shifts that are not favorable for fat loss. This is why binge eating and yo-yo dieting are so detrimental to your health and body composition.
6. To help promote better sleep, eat foods that are slower to digest in your last meal before bed. Dips in blood sugar during the night cause spikes in cortisol that then wake you up. Fats, proteins and fiber are good options to help stabilize blood sugar while you sleep. You should avoid drinking a lot of water in the hours leading up to bed, so you do not have to wake up to use the bathroom. Laying down has diuretic effects and this can lead to multiple bathroom trips that interrupt your sleep.

With this in mind, it is important to understand that it is normal and expected to have metabolic adaptations while in a calorie deficit. Your metabolism is not broken, it adapts to keep you alive. You can also increase your metabolic rate. Your metabolic rate is not fixed, it is adaptive.