WHAT HAPPENS TO OUR METABOLISM WHEN WE DIET
The human body is incredibly adaptive. Our metabolisms are quite literally designed to keep us alive through times of food scarcity and famine and they're quite efficient at doing so. Unfortunately, they haven’t quite adapted as quickly as our modern lives have. Meaning, there's no way to let your body know that you're intentionally reducing calories / restricting food to reduce body fat. The body simply senses starvation, and adapts accordingly.
Once our metabolisms have “adapted”, it can cause immense amounts of frustration and lead you to feeling like your metabolism is broken beyond repair as it becomes less and less responsive to a caloric deficit.
The good news, you are not broken and your body is not in “starvation mode”.
Your body has simply adapted.
The difference between the two is that saying your metabolism is damaged or broken would indicate that it is irreversible. or that you did something wrong. However, once we further understand why these adaptations that have happened and how, we can understand that these adaptations can be changed with time, proper fueling, planning, and patience.
CUE: ADAPTIVE THERMOGENESIS
Metabolic adaptation is also known as adaptive thermogenesis. This is the concept where the body’s energy expenditure drops lower than what would be expected with a basic TDEE (total daily energy expenditure) formula based on weight and activity while dieting. It can also be the alternate scenario where energy expenditure increases more than could be predicted with a TDEE formula while in a caloric surplus. This is in part why we can’t solely rely on calorie calculators to help us reach our goals.
To understand where changes are made to the metabolism, let’s explore what our TDEE is made up of.
TDEE is a combination of exercise activity thermogenesis (EAT), thermal effect of feeding (TEF), non exercise activity thermogenesis (NEAT) and basal metabolic rate (BMR). In the image above you can see a rough estimation of the breakdown of how much these factors influence your overall TDEE.
LET'S BREAK DOWN THE COMPONENTS OF YOUR TDEE:
EAT (Exercise Activity Thermogenesis)
EAT is your dedicated exercise that you participate in. EAT will be influenced by the type of exercise you participate in, the duration of exercise sessions, how intense your training is, etc. EAT likely decreases to an extent during a caloric deficit due to your reduced body mass as you lose weight, and an increase in exercise efficiency, meaning your body adapts to the stress of the training and caloric burn decreases. This is why we love resistance training and are huge advocates of progressive overload.
TEF (Thermal Effect of Food (or Feeding)
TEF is the energy it takes for your body to break down food and assimilate nutrients. Yup, we expend calories by eating and digesting! This will be influenced by overall gut health in general, meal composition, fiber and protein consumption and hydration. During a caloric deficit we can see TEF drop a little due to less food consumption overall. Making sure to eat an adequate amount of protein and fiber can help here a little bit.
NEAT (Non Exercise Activity Thermogenesis)
This is influenced by fidgeting, puttering around the house and your daily steps. Because this makes up the largest part of the energy expenditure we actually have control over, this is why we love being cognizant of our daily steps at Level TEN. When people are in a caloric deficit for an extended period of time, studies have shown that NEAT decreases. People fidget less, overall movement decreases - even natural movements like blinking have been shown to have been reduced - all in the body's efforts to conserve energy.
BMR (Basal Metabolic Rate)
Our BMR is the amount of calories burned at rest. Even if you were to do nothing but lay in bed all day and watch Netflix, your body would still require a substantial amount of calories to keep your organs running and brain functioning. Your BMR is influenced by your hormones, sleep, training status, hydration, body mass, and nutrient availability. The largest factor we see affecting BMR during a caloric deficit are changes to body weight and body composition as weight is lost. A body that has 20lb less on it will require less calories to maintain it.
It’s also worth noting that important hormones that help regulate metabolism and BMR such as thyroid hormones (T3 and T4) and leptin also decrease during an extended period of a caloric deficit.
Does this mean we should never diet?
Nope! This just means that we should consider the frequency and length of time spent in a caloric deficit. There are also some really helpful steps you can take to help mitigate some of the negative metabolic adaptations that occur with dieting. Keep in mind this doesn’t mean we can completely avoid them but we can help reduce them a bit.
Diet on the highest amount of calories possible to elicit positive results. This means avoiding crash diets, 1200 calorie diets, and going harder to get faster results. These strategies will simply encourage your body to adapt faster and leave you with far less wiggle room to adjust calories down in the future. Start with the minimal effective dose. Why reduce your calories by 25% if you can see results with a 10% reduction in calories? Keeping the size of your deficit in check can also help your body retain as much muscle mass as possible and keep your performance higher. Not to mention, you'll simply feel better overall.
Lift heavy things regularly! Adding in resistance training or continuing to resistance train will help your body retain muscle during a deficit. While we likely won't gain loads of muscle in a deficit, at the absolute minimum, we want to work to limit any decreases in muscle mass, or what we call muscle atrophy.
Eat an adequate amount of protein. Most people diet and just slash calories paying no attention to where their calories are coming from. We need an adequate amount of protein to help retain muscle in a deficit. Protein also has the highest thermal effect of feeding, meaning it takes more energy to digest, breakdown and use protein than it does for any other macro nutrient. Protein will also help keep you satiated and reduce cravings.
Don’t diet forever. Keep the length of your deficit in check. Everyone is different in the amount of time they can spend in a deficit which is why working with a qualified coach through the process can be beneficial. Paying attention to biofeedback such as mood, recovery, sleep, stress, energy and hormones such as menstrual health can tell you a lot about how your body is responding to a deficit. After a dieting phase, we want to spend just as long as we were dieting, in a maintenance phase of higher calories. This means eating an adequate amount of food and focusing on not dieting for a bit. Know that sometimes it may take more than one dieting phase to achieve your overall desired results and that is ok and healthy.
Incorporate re-feed days and diet breaks. Refeed days are typically 24-48 hours of increased calories closer to maintenance. Calories are typically increased mainly by carbohydrates. Refeed days are thought to increase leptin (our satiety hormone) and replenish glycogen stores and in turn increase performance and energy. The science on refeed days isn’t conclusive that it is helpful in mitigating metabolic adaptations but we do know they are helpful from a psychological aspect and can give someone a break from the grind of dieting and increase adherence.
Have a plan AFTER your dieting phase. After dieting your body is ready to put on fat to protect you from famine in the future. We also typically see an increase in hunger levels post-diet. This is a perfect combination for weight re-gain, which many people fall victim to. This is why methodically increasing your calories over a few weeks and finding your new maintenance is important. If you just go back to what you were doing before your dieting phase, you will likely gain your weight back. Cue reverse dieting and gradual increases to your intake!
We don’t need to be fearful of dieting, but it is important to understand how it affects our body.
This can help us make educated decisions and understand the importance of taking a periodized approach to our nutrition and practicing patience when it comes to losing fat.
When we have implemented yo-yo diets or have been dieting for as long as we can remember, our metabolisms aren't broken, they've just adapted.
We CAN fix it and with time, we can get to a place where we can maintain our results and eat an adequate amount of food while doing so.
Resources:
https://pubmed.ncbi.nlm.nih.gov/24571926/
https://pubmed.ncbi.nlm.nih.gov/12609816/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7260129/
WITH GOOD VIBES - COACH COURTNEY