Rationale: Currently there is no consensus on protein requirements for obese older adults during weight loss. Here we explore the potential use of a new method for assessment of protein requirements based on changes in appendicular muscle mass during weight loss.
Methods: 60 obese older adults were subjected to 13 wk weight loss program, including hypocaloric diet and resistance training. Assessment of appendicular muscle mass was performed by DXA at baseline and after 13 wk challenge period, and the difference calculated as muscle mass change. Protein intake (g/kg body weight and g/kg fat free mass (FFM)) at 13wks was used as marker of protein intake during 13 wk period. 30 subjects received 10 times weekly 20 g protein supplement throughout the 13 week hypocaloric phase which is included in the calculation of total protein intake. Receiver operating characteristic (ROC) curve analysis was used to explore the optimal cutoff point for protein intake (g/kg) versus increase in appendicular muscle mass of more than 250 g over 13 wks (y/n). Subsequently, logistic regression analysis was performed for protein intake cutoff and muscle mass accretion, adjusted for sex, age, baseline BMI, and training compliance.
Results: ROC curve analysis provided a protein intake level per day of 1.2 g/kg bw and 1.9 g/kg FFM as cutoff point. Presence of muscle mass accretion during 13 wk challenge period was significantly higher with protein intake higher than 1.2 g/kg bw (OR 5.4, 95%CI 1.4–20.6, p = 0.013) or higher than 1.9 g/kg FFM (OR 8.1, 95%CI 2.1–31.9, p = 0.003). Subjects with a protein intake higher than 1.2 g/kg had significantly more often muscle mass accretion, compared to subjects with less protein intake (10/14 (72%) vs 15/46 (33%), p = 0.010). For 1.9 g/kg FFM this was 70% vs 28% (p = 0.002).
Conclusion: This exploratory study provided a level of at least 1.2 g/kg body weight or 1.9 g/kg fat free mass as optimal daily protein intake for obese older adults under these challenged conditions of weight loss, based on muscle mass accretion during the challenge.
Alex’s Notes: With the strong association between excessive adiposity and numerous health complications, weight loss among the obese is a no-brainer regardless of age. However, a potential consequence of weight loss is muscle loss, which in older adults may accelerate the development of sarcopenia. Needless to say, maintaining muscle mass should be a central tenant of any weight loss attempts to not only preserve quality of life but also prevent the deadly feed-forward loop of physical inactivity and impaired mobility.
About a month ago it was revealed that 1.1g/kg of protein, combined with a 12-week resistance training program, was ideal for lean body mass and strength gains in older adults. Specifically, increasing the amount of protein to 1.4g/kg had no advantage over 1.1g/kg. However, although the participants were overweight, the conditions were designed to maintain weight. To thus determine the optimal protein intake for older obese adults dieting for weight loss, the study at hand conducted an analysis of a previously conducted double blind randomized controlled trial in which 60 elderly men and women (>55 years) underwent a 13-week hypocaloric diet (-600 kcal) and resistance training program.
The training took place three times per week over the course of the study, and the participants were divided into two groups: protein supplemented (20g whey) or placebo. In the both groups, the participants had to consume their supplement daily just before breakfast and after each resistance training session (so ten servings per week). Other than this supplement, the diets were largely uncontrolled for with the only advice being to consume a 600 kcal deficit based on estimated energy expenditure. This provided the much needed variation in protein intake that the current study analyzed in combination with the DXA-determined muscle mass measurements.
Using a cutoff point for protein intake based on muscle mass accretion of more than 250g, it was determined that 1.2 g/kg bodyweight (BW) and 1.9 g/kg lean-body mass (LBM) represented the amount needed to prevent muscle wasting. In fact, despite no differences in weight loss among those consuming more or less than this amount, those consuming more had an average of 1.2 kg more muscle accretion than those consuming less.
Something that isn’t mentioned in the text but becomes apparent when looking at the data is the huge inter-individual variability. For instance, one subject consumed 1 g/kg protein and had a loss of 7.5 kg of muscle. Another subject consumed 0.6 g/kg of protein and gained nearly 4 kg of muscle mass. I bring this up solely as a reminder that studies such as this only provide a general baseline to start with.
It is well-known that older adults suffer from anabolic resistance for three main reasons:
- Splanchnic sequestration of amino acids after eating which decreases their availability for muscles,
- Insulin resistance which limits amino acid uptake into muscles and hinders the maintenance of muscle protein, and
- A blunted response to amino acids with anabolic properties, like leucine.
A fairly recent publication by the Obesity Management Task Force of the European Association for the Study of Obesity recommends 1.5g/kg of high-quality protein during a hypocaloric diet for treatment of obese elderly. Taken in conjunction with the current study, it does thus appear that 1.2-1.5g/kg BW is ideal for obese elderly attempting to lose weight.