Whether Low-Carb Diets Cause Muscle Deterioration or Not

Whenever you limit your calories, your body loses a little muscle. This is true on all diets, old-fashioned and low-carb. Some people have claimed that low-carb diets cause more deterioration than normal diets. The following studies measured the amount of protein (muscle) losses that occurred on various diets. As it turns out, low-carb diets cause less deterioration than normal diets.

The human metabolic response to chronic ketosis without caloric restriction: physical and biochemical adaptation.

Phinney SD, Bistrian BR, Wolfe RR, Blackburn GL
Metabolism 1983 Aug;32(8):757-768

To study the metabolic effects of ketosis without weight loss, nine lean men were fed a eucaloric balanced diet (EBD) for one week providing 35-50 kcal/kg/d, 1.75 g of protein per kilogram per day and the remaining kilocalories as two-thirds carbohydrate (CHO) and one-third fat. This was followed by four weeks of a eucaloric ketogenic diet (EKD)--isocaloric and isonitrogenous with the EBD but providing less than 20 g CHO daily. Both diets were appropriately supplemented with minerals and vitamins. Weight and whole-body potassium estimated by potassium-40 counting (40K) did not vary significantly during the five-week study. Nitrogen balance (N-Bal) was regained after one week of the EKD. The fasting blood glucose remained lower during the EKD than during the control diet (4.4 mmol/L at EBD, 4.1 mmol/L at EKD-4, P less than 0.01). The fasting whole-body glucose oxidation rate determined by a 13C-glucose primed constant infusion technique fell from 0.71 mg/kg/min during the control diet to 0.50 mg/kg/min (P less than 0.01) during the fourth week of the EKD. The mean serum cholesterol level rose (from 159 to 208 mg/dL) during the EKD, while triglycerides fell from 107 to 79 mg/dL. No disturbance of hepatic or renal function was noted at EKD-4. These findings indicate that the ketotic state induced by the EKD was well tolerated in lean subjects; nitrogen balance was regained after brief adaptation, serum lipids were not pathologically elevated, and blood glucose oxidation at rest was measurably reduced while the subjects remained euglycemic.

Comments: They gave some men a low-carb diet. They were allowed to eat as much as they wanted, but it had to be low-carb. So this is the Atkins diet. These men were already thin, as it turns out, they didn't lose weight. They measured the amount of protein they were losing by urine testing. They discovered that they weren't losing any.

Protein metabolism during weight reduction with very-low-energy diets: evaluation of the independent effects of protein and carbohydrate on protein sparing.

Vazquez JA, Kazi U, Madani N Department of Medicine, University of Pittsburgh School of Medicine, USA.
Am J Clin Nutr 1995 Jul;62(1):93-103

The aim of this study was to assess the independent effects of carbohydrate and protein intakes in protein sparing during weight reduction. Forty-eight obese women were randomly assigned to consume isoenergetic (2500 kJ/d) liquid diets that provided the following amounts (g/d) of protein and carbohydrate, respectively, for 28 d: 50 and 10, 50 and 76, 70 and 10, and 70 and 86. The effects of carbohydrate and protein were analyzed by repeated-measures analysis of variance (ANOVA). Carbohydrate significantly affected daily urinary ammonia and total nitrogen excretion, stool nitrogen, and nitrogen balance. Protein, independently of carbohydrate, significantly affected daily urinary ammonia, urea, and total nitrogen excretion but had no effect on nitrogen balance. Cumulative nitrogen losses (mmol/28 d) were lower in the high-carbohydrate groups than in the low-carbohydrate groups (1869 +/- 392 and 3611 +/- 328, P = 0.003) but were similar in the groups receiving 50 and 70 g protein/d (3171 +/- 327 and 2326 +/- 430, respectively, P = NS). These results indicate that carbohydrate and protein have independent but additive protein-sparing effects during weight reduction.

Comments: They gave people varying amounts of protein and carbohydrate, and then measured the amount of protein (muscle) they were losing. The more protein they ate, the less muscle they lost. The people who ate 50g of protein lost 3171 units of muscle. The ones who ate 70g only lost 2326 units of muscle. If you extrapolate, you can estimate that if they had received 125g of protein, they wouldn't have lost any muscle. Bear in mind that these numbers are unrealistically high: it takes time to adapt to a new diet, and this study is too short for adaptation to have taken place. The longer-term studies show much lower protein requirement.

Metabolic effects of very low calorie weight reduction diets.

Hoffer LJ, Bistrian BR, Young VR, Blackburn GL, Matthews DE
J Clin Invest 1984 Mar;73(3):750-758

A randomized comparison trial of two very low calorie weight reduction diets was carried out for 5 or 8 wk in 17 healthy obese women. One diet provided 1.5 g protein/kg ideal body weight; the other provided 0.8 g protein/kg ideal body weight plus 0.7 g carbohydrate/kg ideal body weight. The diets were isocaloric (500 kcal). Amino acid metabolism was studied by means of tracer infusions of L-[1-13C]leucine and L-[15N]alanine. After 3 wk of adaptation to the diets, nitrogen balance was zero for the 1.5 g protein diet but -2 g N/d for the 0.8 g protein diet. Postabsorptive plasma leucine and alanine flux decreased from base line by an equal extent with both diets by approximately 20 and 40%, respectively. It was concluded that protein intakes at the level of the recommended dietary allowance (0.8 g/kg) are not compatible with nitrogen equilibrium when the energy intake is severely restricted, and that nitrogen balance is improved by increasing the protein intake above that level. Basal rates of whole body nitrogen turnover are relatively well maintained, compared with total fasting, at both protein intakes. However, turnover in the peripheral compartment, as evidenced by alanine flux, may be markedly diminished with either diet.

Comments: One group was given a harsh diet of only 500 calories, but it was pure protein. The other group was given a harsh diet of only 500 calories, which was a mix of carbs and protein. They did extremely accurate urine tests to check for muscle loss. The carb-eaters lost muscle. The protein-eaters didn't.

Glucose utilization and nitrogen balance in the obese on a protein-lipid hypocaloric diet.

Reid D, Rasio E
Can J Physiol Pharmacol 1982 Mar;60(3):319-323

Glucose utilization and insulin and growth hormone responses were evaluated in eight obese women by three rapid intravenous glucose tolerance tests (IVGTT): during a control period, and after 1 and 3 weeks of a 750 kcal/day protein-lipid diet (1 kcal = 4.1855 kJ). Weight loss averaged 454 g/day during the 1st week and 238 g/day for the 2nd and 3rd weeks of the diet. Nitrogen balance was maintained in equilibrium. Plasma insulin concentrations fell by 50% within 1 week of dieting; growth hormone levels were not modified. The net rate of glucose disappearance dropped from 0.98 to 0.65 and 0.68% min, the glucose pool from 16.2 to 13.3 and 13.4 g, and glucose utilization from 158 to 88 and 87 mg/min during the control period, and at 1 and 3 weeks of dieting, respectively. The insulinogenic index decreased from 0.41 to 0.24 to 0.16 with successive IVGTT's. The glucose volume of distribution was not modified with dieting. It is concluded that a hypocaloric protein-lipid diet induces (i) a carbohydrate intolerance not related to a negative nitrogen balance and (ii) a rapid initial weight loss which cannot be ascribed to a depletion of the glucose volume.

Comments: They gave eight women a low-carb diet that was only 750 calories. Even with so few calories, they still didn't lose any muscle.