In general, you should be eating around or under your BMR. Your basal metabolic rate contributes to 70% of your total energy expenditure. Eating just under your BMR will create 30% of a calorie deficit and with enough consistency trigger weight loss.
But the longer you stay in the calorie deficit, your metabolism can slow down. So if your goal is to lose fat and get a diced look where your abs never go away, you need to cycle your calorie intake.
How Does BMR Help Lose Weight?
Generally, BMR does help with losing weight by providing the estimated amount of calories that need to be consumed to create a negative energy balance. Knowing your BMR can give you the idea of how many calories a day you need to eat to lose weight.
Normally, you can only accurately measure you BMR by either:
- Direct calorimetry
- Indirect calorimetry
Both of those methods are ridiculously accurate but require a strict laboratory setting and professional air-tight chamber to measure heat produce by the body and the rate of oxygen exchange (source).
None of those methods are widely available nor practical. So we have to rely on estimates and predictive equations. Those types of BMR calculators aren’t as precise as calorimetry (even up to 20-30% off) but they are good enough to guess less the number of calories.
You can find the one of the most precise formula in my article How To Use BMR To Lose Weight
Should You Eat Less Than Your BMR To Lose Weight?
As a general rule, you can eat less than your BMR to lose weight. Lowering calories under your basal metabolic rate will put you in the negative energy balance where calorie expenditure exceeds calorie intake. This creates a calorie deficit where the body burns fat for energy.
Basal metabolic rate is the amount of calories your body burns on a daily basis for things like:
- Blood circulation
- Breathing and oxygen transport
- Cellular signaling
- Protein synthesis
- Cognitive processes
Which all comes down to around 70% of total daily energy expenditure (source).
The most “calorie expensive” is lean muscle mass. Because not only they requires more nutrients but also more oxygen. And with more oxygen consumed, you burn more calories.
Eating below your BMR will guarantee you’re in the calorie deficit. Also remember that apart from weight loss, negative energy balance will create other metabolic adaptations.
Eat Below BMR or TDEE?
In general, you want to eat below your BMR, not TDEE. Eating below BMR will more likely create a calorie deficit. Total daily energy expenditure (TDEE) is the total amount of calories used by the body and this equation is calculated by the estimates that can be off by 20-30%.
In other words:
- Eating below TDEE may or may not put you in the calorie deficit
- Eating below BMR will definitely put you in the calorie deficit
Is It Safe To Eat Under Your BMR?
It is safe to eat under your BMR as long as you consume a balanced diet made of protein, carbs, fats, and all vitamins and minerals. Lowering your calorie intake to below BMR level is nothing different than calorie restriction or intermittent fasting.
What Happens If I Eat Under My BMR?
Initially, when you eat under your BMR, your body will start to use fat for energy and cause weight loss. However, over time, the longer you stay in the calorie deficit, the body will undergo metabolic adaptations and the rate of weight loss will drop.
After you already lost a significant amount of weight, the body will respond with lower energy expenditure. This means you won’t burn as many calories as before the weight loss (source).
That happens because:
- You will eat less food so your thermogenic effect of food will decrease
- You have less weight so your body will use less energy to move around
- You have less lean mass so you will consume less oxygen (unless you do strength training)
Will I Lose Weight If I Eat Below My BMR?
On average, you will lose weight if you eat below your BMR. Eating below your basal metabolic rate will cause the body to switch from using external sources of energy (food from last meal) to start using internal sources of energy (stored body fat).
Depending on your weight loss goal, this process can take several weeks or even months. And with a properly designed nutrition plan and regular resistance training, you can not only have better results but also keep on burning calories, without the weight loss plateau.
Adding strength training to your routine can not only help you with adding more energy to the tank but also it can improve your:
- insulin sensitivity (active muscles soak up the glucose from the blood like a dry sponge)
- resting metabolic rate (adding more lean mass will ensure you continue to burn more calories despite calorie deficit)
- glucose metabolism (more glucose will be converted to glycogen)
- blood pressure (studies shows that strength training can decrease blood pressure and perhaps the risk of future CVD development) (source)
- body fat (more lean mass burns more calories so it will enhance the calorie restriction)
- gastrointestinal transit time (strength training can accelerate bowel transit time, especially in previously sedentary people) (source)
What Happens If You Eat Too Few Calories And Work Out
Initially, eating too few calories and work out can help you speed up the process. Low-intensity exercise can suppress the appetite and lower your hunger. However, after a period of time, too much of a calorie deficit can decrease your performance and your energy levels.
It will all depends from your goals.
- If you love to exercise, increase your calorie intake
- If you don’t exercise regularly, lower the calorie intake
You don’t want to overdo your calorie restriction and exercise at the same time. Going too fat too soon can lower the performance, and halt the progress. Your goal is to keep it sustainable.
The Formula 1 car can go ultra-fast, but it can’t go 5000 miles over several years like a family Honda accord. Your goal is long-term success, not overnight juice cleanse.
NOTE: For people who struggle with exercise while on diet, it is much more realistic to improve your NEAT (non-exercise activity thermogenesis).
NEAT is everything that you do during the day. Everything.
- Maintenance of posture
- Leisure activities
- Playing guitar
You would be surprised how many calories can be burned if your all day is filled up with just general being-busy type of activities. The more you move, the more calories you will use.
Does Eating Below BMR Slow Metabolism?
In general, eating below BMR will slow down metabolism. After significant weight loss, the body will start to adapt by lowering the resting metabolic rate, create changes in thyroid and reproductive hormones (reduces testosterone), and lower the thermic effect of food.
In other words, you hit the weight loss plateau.
When you chronically restrict your body from food, it will start to down-regulate certain mechanisms to survive. This of course will lead to lower energy, weaker immune system, mood disruptions and stress.
This process is called metabolic slowdown.
The easy way to overcome that is by doing calorie cycling.
Calorie cycling helps you to alternate your calorie deficit days with normal eating days. It will “trick” the body and prevent from plateau.
The easiest way to do so is having 1-2 days per week of eating normal (maintenance level) calories and 5-6 days calorie deficit when you eat below your BMR.
You can eat below your BMR as long as you have well-balanced diet.
Adding extra strength training and prioritizing protein intake will help you to maintain lean mass and make sure you’re losing fat, not muscle.
After a prolonged period of dieting it is normal to hit the weight loss plateau. To overcome that start doing calorie cycling with alternating normal eating days with dieting days.