Saturday, January 10, 2015

High Protein Diet & Weight Maintenance - Same or Different Benefits? High Metabolic Rate, Increased Satiety, Improved Body Composition Confirm: "You Better Eat Your Protein!"

Scientists ask: High protein for weight loss only or also during maintenance phases?
"Relatively high-protein diets are effective for body weight loss, and subsequent weight maintenance," that's the first half-sentence from the abstract of the latest study from the Maastricht University, Maastricht (Martens. 2014). A sentence that continues with a reference to an important limitation of the contemporarily available evidence: "It remains to be shown whether these diets would prevent a positive energy balance."

Therefore, Martens et al. conducted a study that investigated the effects of high vs. low protein diets during weeks of body weight stability [unfortunately, no RDA group (0.8kg/day) ;(].
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In that, the researchers objective was to determine fullness, energy expenditure, and macronutrient balances on a high-protein low-carbohydrate (HPLC) diet compared with a high-carbohydrate low-protein (HCLP) diet at a constant body weight, and to assess whether effects are transient or sustained after 12 weeks.
Figure 1: Comparison of the relative contribution of protein, carbohydrates and fat to the total energy intake (Martens. 2014).
As you can see in Figure 1, the "high protein diet" is not exactly as "high" as many of you may have expected. With only 35% of the total energy of approximately 2,000kcal (on average) and a mean body weight of 66kg, the total protein intake relative to body weight was "only" 1.89g/kg protein.
The changes in body composition did not reach statistical significance, but the way the protein balance went from 4.1 ± 18.8 g/day to −16.4 ± 11.1 g/day within just one week and stagnated at −11.9 ± 14.1 g/day on the low protein diet clearly suggests that eating a diet that contains only 0.38g/kg body weight protein won't be able to sustain the amount of lean mass you need to function properly.
Compared to the low protein diet, where only 5% of the daily energy requirements were covered with high protein foods and thus only 0.38g protein per kg body weight, that's yet still plenty of protein and enough to have significant effects on the
  • total energy expenditure (TEE) (P = 0.013), 
  • sleeping metabolic rate (SMR) (P = 0.040), and 
  • diet-induced thermogenesis (DIT) (P = 0.027) 
of the male and female study participants. Most importantly, the total energy expenditure was maintained only in the high protein diet group (HPLC), while it significantly decreased throughout the intervention period in the high carbohydrate (HCLP) diet group (wk 1: P = 0.002; wk 12: P = 0.001).
Figure 2: Metabolic effects of high vs. low protein diets (baseline vs. 12-week in % | Martens. 2014)
Similarly, the protein balance varied directly according to the amount of protein in the diet, and diverged significantly between the diets (P = 0.001); and last but not least, unsurprisingly the fullness ratings were significantly higher in the HPLC vs. the HCLP diet group at wk 1 (P = 0.034), but not at wk 12.
Figure 3: High vs. low protein diets have opposite effects on hunger, fullness, satiety and desire to eat w/ measurable effects on body comp. that may become sign. after more than 12 weeks (Martens. 2014).
Bottom line: The study at hand provides the missing evidence that high protein diets have similar beneficial effects during weight maintenance phases as they do during weight loss phases.

Most importantly, a high protein intake of (in this case) 1.89g/kg protein will help you to maintain a high energy expenditure and keep you from eating more than you need, due to its beneficial effects on hunger, fullness, satiety and the desire to eat you can see in Figure 3. What? Ah, yes! There were also decrease and increase in fat and lean mass of 3% and 1%, respectively. These changes in favor of the high protein diet did not reach stat. significance over the course of the 12-week study, but are likely to become sign. after longer periods | Comment on Facebook!
References:
  • Martens, E. A., et al. "Maintenance of energy expenditure on high-protein vs. high-carbohydrate diets at a constant body weight may prevent a positive energy balance." Clinical Nutrition (2014).