Diet & Weight Magazine

Weight Loss and Resting Metabolic Rate

By Dietdoctor @DietDoctor1

What's one of the biggest secrets to maintaining weight loss long term?

It's maintaining your resting metabolic rate (RMR), sometimes called your basal metabolism.

Your RMR is the number of calories you burn daily to sustain your body's normal functions - basics like breathing, pumping blood in your circulation, brain activity, and cellular functions.

Unfortunately, some forms of weight loss can reduce your RMR, which makes it difficult to maintain your weight loss.

In this guide, we show you how to protect your metabolic rate while losing weight in a healthy way.

Spoiler alert: There is one main principle to remember if you want to improve your chances of protecting your RMR with weight loss:

    Build or maintain lean mass by eating adequate protein and doing resistance training.
Weight loss and resting metabolic rate

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Your resting metabolic rate is the amount of energy, or calories needed to sustain your body's basic functions for 24 hours.

RMR is similar to basal metabolic rate (BMR), and these terms are often used interchangeably - although they are not exactly the same. For this guide, we will use RMR.

How to calculate resting metabolic rate

For an accurate assessment of your RMR, you can have it measured with a specialized test called indirect calorimetry.

You can learn more about indirect calorimetry in our podcast with metabolism expert Kirsty Woods.

While indirect calorimetry is the gold standard for measuring your resting metabolic rate, it can be expensive and isn't widely available. Unfortunately, there aren't any inexpensive, at-home ways to precisely measure RMR. The next best alternative is to estimate RMR.

How to estimate resting metabolic rate

There are various calculators you can use to estimate your RMR. As with many calculators, these are general guides and not entirely accurate. They're based on equations that are imperfect for individuals but fairly accurate when looking at averages in large groups of people.

To give you an idea of your RMR, we've illustrated these estimates using the Revised Harris-Benedict BMR equation, for four different body sizes for both men and women:

Estimated RMR (in calories) by age using the Revised Harris-Benedict BMR equation
Estimated RMR (in calories) by age using the Revised Harris-Benedict BMR equation

If you'd like to calculate RMR for your particular age and size, here is the formula behind the above estimates:

Revised Harris-Benedict BMR equation

  • Men: 88.4 + (13.4 x weight in kilos) + (4.8 x height in cm) - (5.68 x age in years)
  • Women: 447.6 + (9.25 x weight in kilos) + (3.10 x height in cm) - (4.33 x age in years)

Some people like to calculate RMR using more than formula, for comparison purposes, as different formulas have been shown to over- or underestimate RMR under different circumstances. A detailed discussion of the advantages and disadvantages of each formula is outside the scope of this guide, but here is an alternative formula you can try:

Mifflin-St Jeor equation

  • Men: (9.99 x weight in kilos) + (6.25 x height in cm) - (4.92 x age in years) + 5
  • Women: (9.99 x weight in kilos) + (6.25 x height in cm) - (4.92 x age in years) - 161

Some of the factors affecting your resting metabolic rate are outside of your control - such as your biologic sex, age, height, and genetics. However, other factors are within your control - such as weight and body composition.

Losing weight can decrease RMR, but losing weight in a healthy way by maintaining lean mass and losing mostly fat mass helps counteract this reduction. You can help maintain or even build lean mass by eating an adequate- or high-protein diet and doing resistance training regularly.

As we detail in our guides on exercise and health and how to improve your body composition, resistance training is the clear winner for building lean muscle mass. Cardio exercise may provide other benefits, like improvement in cardiorespiratory fitness and calorie expenditure (which can lead to fat loss if appetite remains in check), but it's unlikely to help you build muscle like resistance training will.

Studies have also shown that low-carb diets can help people lose mostly fat mass while maintaining both lean mass and resting metabolic rate. However, it's important to note that in many trials the low-carb diet group also tends to eat more protein. So, it may be more accurate to say the data support that a lower-carb, higher-protein diet can help maintain RMR.

To learn more about starting a low-carb diet, we have a great resource: A low-carb diet for beginners.

Some foods, such as coffee, green tea, and capsaicin (the compound that makes some foods spicy, like chili peppers), can reportedly improve metabolism or RMR. However, the data supporting these claims are weak and they are likely not good choices for improving your RMR. You can read more in our guide on fat-burning foods.

Why does resting metabolic rate matter?

Resting metabolic rate is important if you want to know how much to eat to maintain a calorie balance or deficit.

To lose weight you need your daily energy expenditure to be higher than your calorie intake. That doesn't mean you have to count calories. With low-carb, higher-protein diets, people tend to naturally eat fewer calories without counting them. This is due, at least in part, to the satiety effect of protein.

However, when people are struggling to lose weight or hitting plateaus they can't break through, it can be helpful to make sure that calorie intake is less than total daily energy expenditure.

But losing weight with a calorie-restricted diet can be a problem if RMR decreases significantly with weight loss.

RMR tends to go down with weight loss, particularly as lean body mass is lost. However, RMR often drops even further than what would be predicted based on how much lean tissue is lost. This is called metabolic adaptation and has led many researchers to speculate that this extra decline is part of the body's natural defense mechanism to prevent further weight loss.

A study of the contestants from The Biggest Loser TV show demonstrated that the aggressive "eat less, move more" approach resulted in a substantial and lasting reduction to participants' RMR. Six years after the show ended, many of the contestants regained most of their lost weight, and their average RMR was 500 calories per day less than expected, based on their measured body composition and increased age. That is a disastrous combination for long-term healthy weight loss.

The majority of your daily energy expenditure comes from your RMR. Exercise expends energy, but usually only a small percentage of total daily calories. For example, if your RMR is 1,500 calories, and your physical activity burns another 300 calories (roughly the equivalent of walking three or four miles for the average person), your RMR makes up 83% of your 1,800 calorie daily energy expenditure.

In the above example, you need to eat less than 1,800 calories to maintain a calorie deficit.

But what happens to your RMR if you lose 40 pounds?

If a 5 ft. 5 in. (165 cm) 50-year old woman who weighs 200 pounds (91 kilos) loses 40 pounds in a manner that doesn't protect RMR, her RMR will go from 1,583 calories per day to 1,417 calories per day using the Harris-Benedict equation. All of a sudden, she needs to cut 166 calories out of her daily meals just to maintain her weight.

On the other hand, if she's able to maintain her RMR at 1,583 calories per day during weight loss, she won't have to worry about cutting any calories from her diet; she can continue to eat 1,800 calories (assuming 1,583 RMR + 217 physical activity) while remaining weight-stable.

Even if you don't count calories, the concept is still important. If your RMR goes down, you'll have a harder time maintaining weight loss. You can improve your chances of succeeding long-term by either maintaining RMR or preserving as much of it as possible.

Is rapid weight loss always bad for my resting metabolic rate?

The results from the Biggest Loser study may give the impression that rapid weight loss always leads to poor long-term success. Interestingly, studies examining slow versus fast initial weight loss have produced contradictory results, with some suggesting slow and steady wins the race and others showing that rapid loss leads to greater and more sustained weight loss.

The existing evidence is inconclusive with respect to why some people experience greater success with slow or fast initial weight loss. Rapid up-front loss can be reinforcing and encouraging, while a slow rate of loss might be less likely to cause significant metabolic adaptation. Because this is all speculative, we believe the best path is to focus on healthy weight loss, rather than weight loss at any cost.

Healthy weight loss protects your resting metabolic rate

We can't say it enough: we believe weight loss, per se, should not be your ultimate goal. Instead, healthy weight loss should take center stage.

One crucial aspect of healthy weight loss is protecting your RMR.

The traditional "eat less, move more" approach to weight loss often leads to reduced RMR, which means it often leads to unhealthy and unsustainable weight loss.

Eating low-carb, higher-protein foods, combined with regular resistance training, is a great start to maintaining your RMR. This can set you up for success with long-term healthy weight loss.

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