Background – The effects of high protein and high carbohydrate diets on cardiovascular risk factors are inconclusive. Few studies have examined the long-term effects in a free-living population.
Objective – To determine the long-term effects of a high protein versus a high carbohydrate diet on cardiovascular risk factors post-weight loss.
Design – One hundred and forty one overweight and obese subjects who had previously lost >10% of their body weight using a very low energy diet (VLED) for 12 weeks were randomised to a high protein (HP) or high carbohydrate (HC) iso-energetic diet for weight maintenance, or further weight loss if necessary, for 12 months. Outcomes – Both dietary groups maintained their initial weight loss over the 12 month follow-up period. There was no significant difference in weight loss between the dietary groups at any time point. Total cholesterol and triglyceride levels were significantly reduced after the VLED and remained lowered throughout the trial for all subjects. After six months dietary treatment, the HP group experienced a significant increase in High Density Lipoprotein (HDL) cholesterol compared to the HC group (P=0.036). The difference was close to significant at 12 months (P=0.06). Pairwise comparisons across all individuals revealed a significant mean decrease in SBP of 13.5mmHg (P<0.001) from baseline to the end of month 3. After randomization at month 3, no significant difference in mean SBP decrease from baseline was detected between the two groups at this time (P=0.375) or at month 9 (P=0.194). However, by study completion the mean decrease of 14.3mmHg in SBP from baseline for the HP group was significantly larger than 7.7mmHg for the HC group 0 (P=0.045). On average, whilst individuals in the HC group struggled to maintain their initial reduction in SBP, those in the HP group did not.
Conclusion – Despite there being no difference in weight loss achieved by the two dietary groups, the HP diet appeared to confer beneficial effects on HDL cholesterol and SBP in the medium to long-term.
This study was funded by a grant from Meat and Livestock Australia.