Reduced function mutations in the insulin/IGF-I signaling pathway increase maximal lifespan and health span in many species. Calorie restriction (CR) decreases serum IGF-1 concentration by ~40%, protects against cancer and slows aging in rodents. However, the long-term effects of CR with adequate nutrition on circulating IGF-1 levels in humans are unknown. Here we report data from two long-term CR studies (1 and 6 years) showing that severe CR without malnutrition did not change IGF-1 and IGF-1 : IGFBP-3 ratio levels in humans. In contrast, total and free IGF-1 concentrations were significantly lower in moderately protein-restricted individuals. Reducing protein intake from an average of 1.67 g kg(-1) of body weight per day to 0.95 g kg(-1) of body weight per day for 3 weeks in six volunteers practicing CR resulted in a reduction in serum IGF-1 from 194 ng mL(-1) to 152 ng mL(-1). These findings demonstrate that, unlike in rodents, long-term severe CR does not reduce serum IGF-1 concentration and IGF-1 : IGFBP-3 ratio in humans. In addition, our data provide evidence that protein intake is a key determinant of circulating IGF-1 levels in humans, and suggest that reduced protein intake may become an important component of anticancer and anti-aging dietary interventions.

Twenty-six nitrogen balance studies were performed in 15 patients with severe uremia (Ccr mean value 5.1, range 2.3-8.5 ml/min) treated with an unselected protein-poor (16-20 g protein/day corresponding to 2.6-3.2 g N/day) diet and oral supply of the essential amino acids including histidine (2.6 g N/day). The general condition improved and the concentration of serum urea nitrogen decreased. The nitrogen balance, corrected for changes in total urea pool, was negative on the diet alone,-1.46 plus or minus 1.15 g N/day (mean plus or minus SD), but was positive when the essential amino acids were supplied, plus 0.84 plus or minus 0.68 g N/day. In four patients studied after 3 to 26 months of diet and amino acid therapy, during which time a further deterioriation of the renal function had occurred, the nitrogen balance was around zero in three and negative in one patient (-1.2 g N/day). The results show that it is possible with our new regimen to attain positive nitrogen balance or nitrogen equilibrium in severely uremic patients without excessive accumulation of urea in the body fluids.

Twenty-six uremic patients - serum urea nitrogen (SUN) 110 MG/100 ml plus or minus 22.8 (mean plus or minus SD), serum cretinine (S-Creat) 13.2 mg/100 ml plus or minus 2.27, ratio SUN/S-Creat 8.6 plus or minus 2.26, and endogenous creatinine clearance (Ccr) 3.86 plus or minus 1.41 ml/min - were treated for three months or longer with an unselected protein-poor (16-20 g protein/day) diet with oral supply of the essential amino acids including histidine in high doses as coated tablets. The amino acids were instituted after an initial diet only period (mean 0.4 months). The average treatment time was 8.4 months (range 2.7-33.6). An improvement of the general condition was obtained, persisting for several months. SUN and SUN/S-Creat decreased on the diet alone, continued to decrease after one month, and increased slightly again after three months of treatment, but did not reach the initial levels for several months in spite of an almost doubled nitrogen intake. S-Creat increased after six months indicating a further deterioration of the renal function. In patients with initially low serum total protein (smaller than 6.5 g/100 ml, 9 patients), albumin (smaller than 3.5 g/100 ml, 10 patients), and total iron-binding capacity (smaller than 260 mug/100 ml, 11 patients) the values increased after one month on amino acids and were thereafter stable. No signs of bleeding tendency, progressive muscle atrophy, or progressive peripheral neuropathy were observed. - Five patients died due to cardiovascular maladies. A further 13 patients were withdrawn for medical reasons (overhydration, 4 patients; hypertension, 1 patient; nausea and vomiting, 7 patients; and pericarditis, 1 patient). - The renal function improved in one patient. Four patients received home dialysis training, three a kidney transplant. - The results indicate that it is possible to keep severely uremic patients free from uremic symptoms, counteract protein depletion, and even improve the nutritional status during long-term treatment with an unselected protein-poor diet supplementd with essential amino acids.