7-Day Protein-Modified Fast - All the Benefits of Fasting W/Out the Risk of Muscle Loss? Human Study Says...

Lean wild salmon would be a good protein source for a PSMF regimen.
If you are not familiar with the idea of a "protein modified fast" here's what it's all about: in order to minimize the use of lean tissue as a source of energy, a protein-sparing modified fast (PSMF) will combine very low calorie diet with some (often high amounts of) protein, fluids, and vitamin and mineral supplementation.

Matthew Furber and his colleagues from the GSK Human Performance Lab and the University of Hertfordshire and the Anglia Ruskin University were recently able to proof that this special variety of fasting will not only help you shed body fat at a low risk of significant lean mass declines, it will also have profound health benefits.
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As the authors highlight, the past decade of research has demonstrated quite conclusively that a hypocaloric high fat/low carbohydrate (HF/LC) diet can up-regulate transcriptional markers of mitochondrial biogenesis; accordingly, this is what the scientists based their subjects' diets on.
Figure 1: Macronutrient comp. of the diets (for both, the EM = maintenance +ER = calorie restricted diets | Furber 2017)
Forty-five healthy male participants were randomly assigned one of four intervention diets: eucaloric high-protein (PRO-EM), hypocaloric high-protein (PRO-ER), eucaloric high-carbohydrate (CHO-EM) or hypocaloric high-carbohydrate (CHO-ER). The macronutrient ratio of the high protein diet and high carbohydrate diets was 40:30:30% and 10:60:30 % (PRO:CHO:FAT) respectively. The "[e]nergy intake for the hypocaloric diets were calculated to match resting metabolic rate" (Fuber 2017).

Ok, I know this is not a "fast", but I stick to the term, 'cause the authors use it

Participants visited the laboratory on 3 occasions each separated by 7 days. On each visit body composition, resting metabolic rate and a muscle biopsy from the vastus lateralis was collected. Prior to visit 1 and 2, the subject simply consumed their habitual diet, which thus served as a control. Between visit 2 and 3, the intervention diet was consumed continuously for 7-days.
Figure 2: The scientists observed increases in AMPK, Sirt1+3 and PGC-1a, proteins that mediate the health benefits of fasting and, compared to the high-CHO fast, a sign. reduced lean mass loss + slightly enhanced fat loss (Furber 2017).
The scientists' analysis of the data shows that, in the PRO-ER group, a significant increase in
AMPK, PGC-1α, SIRT1 and SIRT3 mRNA expression was observed - a slightly greater increase than in the other groups, that is (p < 0.05).

Furthermore, no difference in lean mass (LM) loss was observed between the PRO-ER and CHO-EM groups, despite ~30 % reduction in calorie intake - and that's just what the many N=1 reports on the results of short-term PSMF regimen say, as well.
The high protein content of the diet also kept the resting metabolic rate (RER) of the subjects elevated. The RER of the subjects dieting on a high carbohydrate diet, however, declined by 4.3% (Furber 2017).
What does that mean, practically speaking: The study at hand may confirm that a 40:30:30% (PRO/CHO/FAT) diet consumed for 7 days will shed significant amounts of body fat while having less of a negative impact on your lean mass than its high(er) carbohydrate cousin. Furthermore, the high protein way of dieting ameliorated te effect of protein on the diet-induced reduction in energy expenditure (RMR +2% in PRO-ER vs. RMR -4% in CHO-ER.

That's all great new, but it's not worth the virtual paper it was printed on. After all, even if a loss of glycogen made the results look extra bad, a ratio of lean to fat mass loss of almost 1:1 is unbearable. You can do better and I've pointed out how in previous articles like this one | Comment!
  • Furber M, Anton-Solanas A, Koppe E, Ashby C, Roberts M, Roberts J. "A 7-day high protein hypocaloric diet promotes cellular metabolic adaptations and attenuates lean mass loss in healthy males." Clinical Nutrition Experimental (2017), doi: 10.1016/j.yclnex.2017.05.002.
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