Do Low Carb or High Carb Diets Preserve Muscle Better?

August 4th, 2010 by Paul Johnson

I’ve always been skeptical of Low Carb Diets for the average bodybuilder, unless they are getting ready for a competition. Low carb diets are needed for competition condition so they come in very dry. It’s almost been accepted as fact in the bodybuilding community for years that low carb diet was the quickest way to lose muscle, especially if you are a hardgainer. Recent bodybuilding authors like Lyle Mcdonald, who is making low carb diets very popular and new studies released, may prove that high carbs are not the best after all.

Low carb diets vs. high carb diet metabolism

In high carb diets you generally eat around 40 percent of your calories from carbohydrates. There are different Low Carb Diets usually called keto diets for bodybuilders, but most like the TKD (Targeted Keto Diet) has you eat about 10 percent of your calories as carbs and you cycle carbs at certain times and days. Instead low carb diets eat a lot more protein and fat to make up for the loss in carbs.

During High carb diets your body continues to metabolize macronutrients as usual, using glucose from carbs mainly for energy. With very Low Carb Diets your glycogen levels would get very depleted extremely fast with the lack of carbs shuttling glucose into your muscles. Your body has to come up with an alternative energy source to preserve some of that glycogen in your muscle for your brain, which needs glucose from the bloodstream. It does this by entering ketosis, where fat sources are used to make ketone bodies. Your brain tends to prefer glucose so that is mainly reserved for brain, while ketone bodies are burned for energy for other activities. Glycogen in the muscles won't be completely depleted either, especially when carb load up days are utilized like in the TKD diet. Therefore during your weight training days you can use glycogen from your muscles for short term energy.

Studies on Low carb and muscle preservation and fat loss

There seems to be studies supporting both sides of the argument when it comes to muscle preservation. Many studies show low carbs preserving muscle better during diet than high carb diets and many studies say the complete opposite too. Here is just 3 studies I want to go over.

The study below shows a simultaneous fat loss and significant muscle gain while dieting low carbs. There was also lower insulin levels in the low carb diet. No other hormonal changes between the two groups such as testosterone or cortisol.

Volek JS, Sharman MJ, Love DM, Avery NG, Gomez AL, Scheett TP, Kraemer WJ: Body composition and hormonal responses to a carbohydrate-restricted diet.

Twelve healthy normal-weight men switched from their habitual diet (48% carbohydrate) to a carbohydrate-restricted diet (8% carbohydrate) for 6 weeks and 8 men served as controls, consuming their normal diet. Subjects were encouraged to consume adequate dietary energy to maintain body mass during the intervention.

Fat mass was significantly (P less than r=.05) decreased (-3.4 kg) and lean body mass significantly increased (+1.1 kg) at week 6. There was a significant decrease in serum insulin (-34%), and an increase in total thyroxine (T(4)) (+11%) and the free T(4) index (+13%).

There were no significant changes in glucagon, total or free testosterone, sex hormone binding globulin (SHBG), insulin-like growth factor-I (IGF-I), cortisol, or triiodothyronine (T(3)) uptake, nor were there significant changes in body composition or hormones in the control group. Thus, we conclude that a carbohydrate-restricted diet resulted in a significant reduction in fat mass and a concomitant increase in lean body mass in normal-weight men, which may be partially mediated by the reduction in circulating insulin concentrations.

The study below shows that most of the loss in weight was due to fat and not muscle on a low carb diet.

Willi SM, Oexmann MJ, Wright NM, Collop NA, Key LL Jr: The effects of a high-protein, low-fat, ketogenic diet on adolescents with morbid obesity: body composition, blood chemistries, and sleep abnormalities.

Six adolescents, aged 12 to 15 years, weighing an average of 147.8 kg (range, 120.6-198.6 kg) and having an average body mass index of 50.9 kg/m (39.8-63.0 kg/m), consumed the K diet for 8 weeks. Daily intake consisted of 650 to 725 calories, which was substantively in the form of protein (80-100 g). The diet was very low in carbohydrates (25 g) and fat (25 g). This was followed by 12 weeks of the K diet plus two carbohydrates (30 g) per meal (K+2 diet)

Dual-energy x-ray absorptiometry showed a decrease from 51.1% +/- 2.1% body fat to 44.2% +/- 2.9% during the K diet and then to 41.6% +/- 4.5% during the K+2 diet. Lean body mass was not significantly affected.

The study below measured protein breakdown at the site and found no difference between low carb and high carb.

Vazquez JA, Adibi SA: Protein sparing during treatment of obesity: ketogenic versus non-ketogenic very low calorie diet.

Metabolism 1992 , 41:401-14. OpenURL

The following study showed that the higher carb diet lost less total fat and lost more muscle (ie. a larger percentage of their weight gains lost were muscle instead of fat)

Young CM, Scanlan SS, Im HS, Lutwak L: Effect of body composition and other parameters in obese young men of carbohydrate level of reduction diet.

They compared three diets containing the same amounts of calories (1,800 kcal/day) and protein (115 g/day) but differing in carbohydrate content.

After nine weeks on the 30-g, 60-g and 104-g carbohydrate diets, weight loss was 16.2, 12.8 and 11.9 kg and fat accounted for 95, 84, and 75% of the weight loss, respectively

These are just some of the studies supporting low carb diets are better at preserving muscle. There are many others out there. There is also many studies out there that show high carbs preserved muscle better.

Final conclusion on low carb vs. high carb

One common denominator from most of the studies I have come across is that Low Carb Diets are a better fat burner. Regardless if one preserves muscle better than the other, if fat loss is your number one concern than low carb diet is the best way to go. That has been the general consensus among bodybuilders for years anyways. The muscle preservation part is more controversial theory I believe. If you're a hardgainer or your muscle genetics aren't that good then it matters a lot more whether or not low carb diets or high carb diets are better in regards to preserving muscle. From all the studies I've seen its really hard to tell which side is right if you don't do some further digging. Even Lyle Mcdonald in his book on keto diets the biggest advocate of low carb diets for bodybuilders, suggests that the results vary and that some lose muscle on low carb and for some its the opposite. Not exactly the most assuring assessment from the number one advocate in the industry.

The other thing I've noticed is most of these studies weren't done on people who weight train. I believe that when someone is working out hard with weights 3+ times a week, the lack of carbs could be a game changer. Carbs give you plenty of energy and strength by keeping your glycogen levels full. When they get depleted more in low carb diets, its much harder to maintain strength and endurance. As you lose strength and do less reps week after week as you get fatigued easier its much harder to hold onto your muscle since they aren't getting the same stimulation so your muscles are going to shrink.

The other reason I'm skeptical that Low Carb Diets hold onto muscle better than high carb diets is insulin is the most potent anabolic hormone in the body. Most people don't realize this, they usually think of Testosterone first. Insulin increases protein synthesis and stops muscle breakdown by up to 50 % (University College London 2006 (2006) Proc Physiol Soc 3, C46) and helps shuttle nutrients into the muscles. Its hard for me to believe that when your eating mainly protein and fat which have very little impact on insulin compared to carbs, you can hold onto your muscle to the same degree. Insulin also counteracts cortisol the main culprit for muscle breakdown.

Could both sides be right?

Lower insulin levels have been shown in these studies for those on Low Carb Diets. They also show no changes in cortisol or other hormones between the two groups that may have an effect. Insulin resistance does lead to poor nutrient partitioning (higher bodyfat percent). Your body doesn't burn fat as effectively or build muscle as well when you don't respond to insulin and become resistant. As said earlier insulin is a potent anabolic hormone and if your body becomes resistant to it your fat loss should be less and your more likely to burn muscle instead.

Perhaps the insulin sensitivity changes in low carb diets are enough to overcome the other obstacles of a low carb diet and actually lead to better fat loss and muscle gains. If someone is borderline diabetic or has a lot of insulin sensitivity due to be overweight or genetics, then perhaps the switch to low carb diets puts their body into a different shift primed for not only losing fat better, but even sometimes gaining muscle. Perhaps this is why results vary between individuals. If someone is presently insulin resistant than low carb diet may be a better option.

Other possible reasons to avoid low carb diets

Whether or not Low Carb Diets works better for fat loss or muscle preservation, some choose to not do them because the risks outweigh any slight gains. I think low carb diets are much harder to stick to long term. What good is a diet if you can't stick to it? Its very hard to come up with a diet for months or years that relies on mainly food that isn't carbs. Also it is very hard to get enough fiber in your diet with such a low carb diet. Low fiber leads to constipation and increased risk of cancer. I also worry about the long term health effects on the body of such low carbs. Low carb diets also make you lose massive amounts of water weight which can give you the false impression of more fat lost than you really lost. You will be dissapointed when you carb back up and gain a lot of that water weight back giving you a more bloated fat appearance.