What Low-Carb Diets Do

March 19, 2010

In response to a recent post, a reader asked the following question: “Are those on those [low carbohydrate] diets losing fat, muscle, water or exactly what because they seem to lose weight?”

iStock_000002664912XSmallFirst, something to keep in mind about ANY diet is that if a diet reduces your calories below what your body needs to maintain itself, you will experience weight loss.  Therefore, low carbohydrate diets that reduce the body’s caloric input below the number of calories it burns will cause weight loss for the low-carb dieter.  All of what follows assumes the low carb diet is low enough in calories to cause a calorie deficit.

Regarding caloric deficits, they may be easier to achieve on a low-carb diet.  Why?  Because it takes a good deal of energy to digest protein.  When we eat protein, the body may burn 25% of the calories in it just to digest it!  So, it may be possible to eat more calories as protein than you would from carbs or fats, and still achieve a calorie deficit.

Low-carb diets force the body to use fat and protein for energy.  Thus fat and protein WILL be used.  That fat will come from fat in the diet as well as from the body’s fat stores, which means the low-carb dieter will lose body fat.

iStock_000002345256XSmallIn a low-carb diet, protein will be used for energy as well.  The protein will come from protein in the diet as well as, possibly, from the body’s protein stores (muscle).  Thus, in a low-carb diet, the stage will be set for some muscle loss.  The longer a person stays on a low-carb diet, and the greater the calorie deficit, the more muscle will be sacrificed.

iStock_000008803211XSmallWhen the body uses protein as fuel, it first breaks the protein down into the amino acids it’s comprised of.  Then the amino acid molecule loses its nitrogen in the liver, which forms urea.  Urea is flushed out of the body in urine, which requires water.  So, excessive use of protein for energy causes water loss.  The person on a low carbohydrate diet can expect lots of weight loss from water loss…even to the point of dehydration if they’re not careful.  The initial weight loss from a low carb diet will come largely from dehydration.

Another thing to keep in mind is that a low-carbohydrate diet, like any “extreme” type of diet, is one that a person is not likely to continue for a great length of time.  Because of this, it is quite likely that the weight a person loses on a low-carb diet will be regained after the person begins to eat “normally” again.

iStock_000006098980XSmallHowever, despite some of the negatives, low carb diets are used effectively in some situations.  Bodybuilders use low carbohydrate diets to “finish” off their contest diets.  Also, these types of diets can be used to break plateaus for carbohydrate “sensitive” individuals that have been eating clean and exercising faithfully, but not achieving desired fat loss of 1 – 2 lbs. per week.  However, for carb sensitive folks, moderately reducing carbs should be enough to achieve desired results.  Extreme carbohydrate reduction is usually not needed.

Hope this clears some of the fog regarding low carbohydrate diets.


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2 Responses to “What Low-Carb Diets Do”

  1. You are so right. Diets do tend to backfire in the long run because the body slows the metabolism. We should just be consistent in eating nutrient rich foods that are low in calories and easy to digest and eat them often throughout the day. We should also exercise in a varied fashion on a regular basis. And keep our stress and therefore cortisol levels down.


  2. Hi Darryl,

    Thank you for those excellent reminders about how with low (refined) carb diets we are also eating some body muscle. Because of 1. having had bariatric surgery 3 yrs ago plus 2. family predisposition for diabetes, we tend towards an Atkins/South Beach diet for when we need to focus on weight loss/release.

    However, I do combine that with significant exercise. I’d put on 10 lbs and am now down 6 lbs (yeah!). Using the apartment complex mini gym and recently joined 24 HR Fitness. Indeed, fitness and health is one of my BF’s greatest interests, we just so different things at the gym. It is just cool both to be there at the same time.

    As always….

    Happy Dating and Relationships,

    April Braswell
    Baby Boomer Dating Expert



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