T Nation

Low Protein: What's (+/-SD) Mean?

Just wondering what (+/-SD) means it’s under results…

4 December 2001 | Volume 135 Issue 11 | Pages 965-976

Background: Chronic renal insufficiency leads to muscle wasting, which may be exacerbated by low-protein diets prescribed to delay disease progression. Resistance training increases protein utilization and muscle mass.

Objective: To determine the efficacy of resistance training in improving protein utilization and muscle mass in patients with chronic renal insufficiency treated with a low-protein diet.

Design: Randomized, controlled trial.

Setting: Tufts University, Boston, Massachusetts.

Patients: 26 older patients with moderate renal insufficiency (17 men, 9 women) who had achieved stabilization on a low-protein diet.

Intervention: During a run-in period of 2 to 8 weeks, patients were instructed and their adherence to the low-protein diet (0.6 g/kg of body weight per day) was evaluated. They were randomly assigned to a low-protein diet plus resistance training (n = 14) or a low-protein diet alone (n = 12) for 12 weeks.

Measurements: Total body potassium, mid-thigh muscle area, type I and II muscle-fiber cross-sectional area, and protein turnover.

Results: Mean protein intake was 0.64 +/- 0.07 g/kg per day after stabilization. Total body potassium and type I and II muscle-fiber cross-sectional areas increased in patients who performed resistance training by a mean (+/-SD) of 4% +/- 8%, 24% +/- 31%, and 22% +/- 29%, respectively, compared with those who did not. Leucine oxidation and serum prealbumin levels also improved significantly. Patients assigned to resistance training maintained body weight compared with those who were not. Improvement in muscle strength was significantly greater with resistance training (32% +/- 14%) than without (-13% +/- 20%) (P < 0.001).

Conclusion: By improving muscle mass, nutritional status, and function, resistance training seems to be effective against the catabolism of a low-protein diet and uremia in patients with renal failure.

It means +/- 1 standard deviation: measurement of statistical dispersion

Under the assumption that the data are normally distributed (form a ‘bell curve’ around the expected value), then 66% of the data lie within 1 standard deviation.