Nope. Dieting does not damage your metabolism. Thanks for coming out, that's all I have for you today. Just kidding! But seriously, dieting damages your metabolism about as much as painting your house ruins the walls. Dieting changes your metabolism but it does not damage it. In today's post (at the request of a reader!) we get to the bottom of what happens to your metabolism when you lose weight.

In your worldly travels you have likely met someone who has lost weight. In rare circumstances you may have met someone who lost weight and kept it off. More likely, said person lost weight and regained it. They may have even gained more weight back than they ever lost. Yikes! I trust you, and I believe you are not naive enough to think your coworker/friend/relative did this on purpose. No one in their right mind goes through the struggle of losing weight only to choose to gain it all back. So why does it happen? If you are fortunate enough to have a body builder in your life (someone who actively competes in aesthetics), they have likely spun you a few yarns about their friend in the industry who "ruined" his or her metabolism by dieting for a show. If you are truly blessed, you will know someone who gets their jollies in by explaining, in detail, their weight loss/regain/loss "journey" with you. In all seriousness, a lot of people struggle with weight loss and I wish we talked more thoughtfully about it more often. Social media "transformation" photos are great, your coworker's impressive pre-prepared meals are great, but weight loss and more importantly, weight maintenance is really hard. Photos of meals in tupperware on Instagram don't tell the full story.

Let's start by talking about metabolism

Your metabolic rate is the total amount of energy produced and used by your body per unit of time (Seeley, Stephens, & Tate, 2008). The amount of energy you put into your body should equal the amount of energy your body expends, otherwise you will gain or lose weight. Your body produces energy (ATP) at about the same rate it is used (Seeley, Stephens, & Tate, 2008). Since most ATP production involves the use of oxygen, metabolic rate is measured by estimating the amount of oxygen your body uses per minute. Your metabolic rate has three components: basal metabolic rate (BMR), the thermic effect of food, and muscular activity.

Your BMR is the amount of energy needed to keep your body functioning at rest (Seeley, Stephens, & Tate, 2008). BMR accounts for 60% of total daily energy expenditure (TDEE). Basically, your BMR is the number of calories your body needs to survive...even if all you did was lay in bed all day. Sounds like a win right? Yes, you actually need calories just to sit on the couch. There are a few factors that can affect your BMR. Muscle tissue is more metabolically active than adipose tissue (even at rest) so the more lean mass you have, the higher your BMR. Plug: do your resistance training! Increasing your muscle mass (not tone ladies) will increase the number of calories your body needs at rest! Do it, do it, do it. Men have proportionally more muscle mass and less adipose tissue than women and thus get to enjoy a higher BMR. Ever wonder why your boyfriend can eat a whole pizza and still have a six-pack? Meanwhile you glance at a pepperoni and your pants feel instantly tighter. Yep, another one of the joys of being female. Younger people will also have a higher BMR than older people because of increased cell activity during growth (Seeley, Stephens, & Tate, 2008). Those enjoying the symptoms of a raging fever will also experience an increase in their BMR. In fact, for each degree Fahrenheit increase in body temperature your BMR increases by 7%! (Seeley, Stephens, & Tate, 2008). Would not recommend this approach to boosting your BMR though... Finally, BMR can increase by 20% during pregnancy because of the increase in metabolic activity of the growing fetus (Seeley, Stephens, & Tate, 2008)! So if fever and pregnancy aren't available options for you, you're stuck with resistance training to boost your BMR. Don't make me say it...obviously I don't advise getting pregnant or feverish just to eat more...

The thermic effect of food is the energy it takes to ingest and digest food and accounts for around 10% of your body's TDEE (Seeley, Stephens, & Tate, 2008). Not all of the energy your body can derive from a meal is stored for later use. Some of the energy is used as the meal is digested and absorbed leaving slightly less energy than you took in for storage. Different nutrients have different thermic effects. Your body uses 0 to 3% of the energy from fat during digestion and absorption, 5 to 10% for carbohydrate, 20 to 30% for protein (Acheson, 1993), and 10 to 30% for alcohol (Westerterp, Wilson, & Rolland, 1999) . When you digest fat, more of it makes its way into energy storage because less of it is used in the breakdown and conversion process than for carbohydrate, protein, or alcohol. That doesn't make dietary fat the enemy, it just makes protein sound like a real pain in the a$$ for your body to digest and absorb. Be that as it may, high protein diets are important to maintain fat-free mass while dieting (Westerterp-Plantenga, 2003). The bottom line is that you have no control over the thermic effect of food. Meals that are rich in lean protein and carbohydrate have a higher thermogenic effect than fatty meals but the significance of thermogenesis in terms of energy expenditure pales in comparison to your body's main energy expenditure: muscular activity.

Your body's muscular activity accounts for 30% of your body's TDEE. The energy you lose through physical activity is the only component of TDEE that you can control. Sure, you can change your diet to eat more lean meats and less fat but you can't change the thermic effect of the food you consume nor do you have any say on what your body's BMR is (indirectly you can lose/gain weight to change it but you don't get to pick the number of calories it takes to power your body at rest!). The amount of energy expended through physical activity is dependent on the amount of muscular work performed and the duration of the activity (Seeley, Stephens, & Tate, 2008). Although listening to your spouse talk about work can make you feel tired....there is little muscular activity at play and thus limited energy expenditure...i.e. little to no change in BMR. Plug #2: lifting weights requires a significant amount of muscular activity and thus increases your metabolic rate! Hey now! You should lift weights! Now that you are up to speed, let's find out how and why your metabolism changes when you lose weight.

Have you ever heard of "Set Point Theory"?

The basic idea is that your body has a preferred weight and level of fatness. Your body, not unlike myself, hates change. From an evolutionary standpoint, this was a good thing. During long periods of energy deprivation (aka when the hunters sucked at hunting and the gatherers had to gather enough twigs and berries to feed the entire village....) it would have been handy to store energy as fat really efficiently. Nowadays, when you can't swing a cat without hitting a Tim Horton's, the advantage of being able to store fat in seemingly limitless quantities is not so hot.

When you lose weight, your body does everything it can to get it back.

Believe it or not, weight loss is not as simple as calories in < calories out. There are a host of genetic, environmental, and physiological factors at play. Whether you are a lean or obese individual, the amount of energy your body stores as fat is regulated by your central nervous system (Rosenbaum & Leibel, 2010). Your ability to maintain a lower body weight is governed by powerful neuroendocrine, metabolic, and autonomic system responses (Rosenbaum & Leibel, 2010). The actual phenomenon some people refer to as "metabolic damage" is likely what is known as adaptive thermogenesis.

Basically, when you lose weight your body responds by reducing your energy expenditure. A 10% reduction in body weight in lean or obese individuals results in a 20-25% decrease in daily energy expenditure (Leibel, Rosenbaum, & Hirsch, 1995; Weigle, Sande, Iverius, Monsen, & Brunzell, 1988). This means that someone who diets down to 150lbs will require less energy to stay at 150lbs than someone who has always weighed 150lbs. Your body actively opposes weight loss. Long-term studies of subjects who were able to sustain their new body weight still had a reduced energy expenditure up to 7 years later (Leibel, & Hirsch, 1984; Van Gemert et al., 2000; Weyer et al., 2000). In fact, the more weight you lose, the greater the reduction in your metabolic rate (Camps, Verhoef, & Westerterp, 2013).

Let's pause for a moment.

When you lose weight, it would make sense that your BMR drops....you are physically made of less matter than you were before...it follows you would need less energy. The problem is, the energy required to maintain your new weight is 10-15% below what would be predicted on the basis of losing fat and lean mass alone (Rosenbaum & Leibel, 2010). In other words, the metabolic rate you have at your new weight is lower than what you should have. In a way, your body betrays you. Keep in mind, if we were to face an apocalypse you'd be really pleased with your body's ability to resist weight loss.

Most of what we know about successful weight loss and maintenance comes from the National Weight Control Registry, a database of 4000 adults (97% Caucasian, 80% women) in the U.S. who have lost at least 30lbs and kept it off for at least 1 year (Sumithran, & Proietto, 2013). Self-reported strategies for maintaining weight loss include: eating a low calorie and low fat diet with minimal variety in food groups with no variance on weekends or holidays (wow!), eating breakfast every day, weighing yourself at least once a week, limiting TV viewing, and engaging in 1 hour of exercise every day (Wyatt, Phelan, Wing, & Hill, 2005). Pretty simple eh? Just fish, salad, water, vigorous exercise, no Netflix, and make sure you never stop weighing yourself. Good grief. The good news is, if you regain back all that weight you worked so hard to lose, your metabolic rate shoots right back up to where it should be (Camps, Verhoef, & Westerterp, 2013). Thankfully, our old friend physical activity plays a big role in preventing weight gain while also helping in weight loss maintenance.

According to a position statement by the American College of Sports Medicine (2009), 150-250 minutes of moderate intensity physical activity is sufficient to prevent weight gain greater than 3% in most adults and may even result in modest weight loss (Donnelly et al., 2009). Well, what do ya know? Physical activity can prevent the cost of inflation....har har. Physical activity in addition to caloric restriction may result in additional weight loss however the additive effect diminishes with more severe caloric restriction (Donnelly et al., 2009). Physical activity may prevent weight regain however the evidence base is limited. Likely there is a dose-response relationship between increased physical activity (in the range of 250-300 minutes per week), increased weight loss, and enhanced prevention of weight regain. It is important to note that as little as a 3% reduction in weight loss can have significant and clinically meaningful changes in chronic disease risk factors (Donnelly et al., 2009). When it comes to weight loss, it's not "go big or go home".

In summary

When you restrict calories to lose weight your body will fight back. The more weight you try to lose, the more dramatic the resistance. You may think reaching your goal weight is the hardest part of dieting, however maintaining your weight may prove to be even more difficult. Your body has a preferred level of fatness dictated by your genetics. Though everyone is capable of losing or gaining weight, it is not as simple as calories in vs calories out. Your body takes weight loss very seriously governing the process through physiologic and hormonal changes that are out of your control.

The problem with reducing your calories to lose weight is that eventually you will run out of calories to reduce! Instead, start with a modest caloric deficit and use exercise to increase your energy expenditure. Don't punish yourself, just eat a bit less and move a bit more until the scale refuses to budge. At that point you can take a step back, introduce a few more calories into your diet until the scale starts moving again. Believe it or not, you may gain a bit of weight back before you start losing it again. Settle in and accept that change takes time. Don't forget to give yourself plenty of self-care along the way. Loving and accepting your beautiful, healthy body goes a long way to keeping stress levels down and freeing up plenty of wasted energy and time.

Take home points

Here are a few evidence-informed strategies for increasing your chances of successful weight loss and maintenance:

Consuming a high protein diet (20-30%) of intake
- Higher thermic effect of food (less bioavailable)
- Increases satiety
- Supports the maintenance of lean mass
Including resistance training in addition to aerobic exercise
- Increases lean muscle mass
- Improves chronic disease risk factors
Combining caloric restriction with physical activity to create an energy deficit (not relying on diet alone)
- Takes a lifestyle approach to weight loss
- More likely to adhere over the long-term
Aiming for a modest reduction in weight (<10%)
- Clinically meaningful in terms of disease risk factors
- Less resistance from your body's hell-bent, anti-weight loss cause

In conclusion...

Your metabolism isn't "damaged" by dieting, it's changed. Your body is an expert in survival tactics which is really great! It just means Plan A has to be preventing weight gain in the first place, and Plan B has to be reducing body weight by a reasonable amount over a reasonable amount of time.

As always, I'm happy to keep the dialogue going through the comments here or via email at: coachpeachey@gmail.com.

Cheers,

Coach P.

References

Acheson, K.J. (1993) Influence of autonomic nervous system on nutrient-induced thermogenesis in humans. Nutrition, 9(4): 373-80.

Camps, S.G.J.A., Verhoef, S.P.M., & Westerterp, K.R. (2013). Weight loss, weight maintenance, and adaptive thermogenesis. American Society for Nutrition, 97: 990-994

Donnelly, J. E., Blair, S. N., Jakicic, J. M., Manore, M. M., Rankin, J. W., & Smith, B. K. (2009). American College of Sports Medicine Position Stand. Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults. Medicine and science in sports and exercise, 41(2), 459-471.

Leibel, R., & Hirsch, J. (1984). Diminished energy requirements in reduced obese patients. Metabolism, 33: 164–170.

Leibel, R., Rosenbaum, M., & Hirsch, J. (1995). Changes in energy expenditure resulting from altered body weight. New England Journal of Medicine, 332: 621-628

Rosenbaum M., & Leibel, R.L. (2010). Adaptive thermogenesis in humans. International Journal of Obesity, 34: S47-S55.

Seeley, R.R., Stephens, T.D., & Tate, P. (2008). Nutrition, Metabolism, and Temperature Regulation. Anatomy & Physiology (8th ed.), pp. 927-960. New York, NY: McGraw-Hill.

Sumithran, P., & Proietto, J. (2013). The defence of body weight: a physiological basis for weight regain after weight loss. Clinical Science, 124(4): 231-241

Van Gemert, W., Westerterp, K.R., Acker, B.A., Wagenmakers, A.J., Halliday, D., Greve, J. et al. (2000). Energy, substrate and protein metabolism in morbid obesity before, during and after massive weight loss. International Journal of Obesity, 24: 711-718

Weigle, D., Sande, K., Iverius, P., Monsen, E., & Brunzell, J. (1988). Weight loss leads to a marked decrease in non resting energy expenditure in ambulatory human subjects.

Westerterp, K.R., Wilson, S.A., & Rolland, V. (1999) Diet induced thermogenesis measured over 24 h in a respiration chamber: effect of diet composition. International Journal of Obesity and Related Metabolic Disorders, 23(3): 287-92.

Westerterp-Plantenga, M.S. (2003). The significance of protein in food intake and body weight regulation. Current Opinion in Clinical Nutrition Metabolic Care, 6 (6): 635-8.

Weyer, C., Walford, R., Harper, I., Milner, M., MacCallum, T., Tataranni, P. et al. (2000). Energy metabolism after 2 y of energy restriction: The biosphere 2 experiment. American Journal of Clinical Nutrition, 72: 946-953

Wyatt, H. R., Phelan, S., Wing, R. R., & Hill, J. O. (2005) Lessons from patients who have successfully maintained weight loss. Obesity Management, 1:56–61

Can dieting damage your metabolism?