Some relatively new research has shown that BCAA (leucine, isoleucine and valine) restriction is responsible for the weight loss seen in protein restricted (PR) diets. As opposed to calorie restricted (CR) diets, the metabolic rate doesn't decrease as happens in CR and in some cases it seems weight loss is accelerated when extra calories are consumed. Most of the studies are in rodents, but some are in people. Some very recent research (Nov 2023) has narrowed it down to just 1 of the 3 BCAAs, isoleucine.

Brad from fireinabottle.net and @exfatloss from Twitter/X have been covering the research. I'll summarize the research and relate it to Ray's general advice for weight loss.

Only BCAA supplementation for inhibiting serotonin has been advocated on the RPF. But maybe getting adequate calcium is as good for lowering serotonin. Without calcium, tryptophan goes to serotonin, with adequate calcium, it goes to niacin.

Its been known for a while that the obese have high circulating BCAAs. In studies comparing lean vs obese people under a weight loss protocol, the lean burn more protein as fuel than the obese. This is also seen in animals during torpor, where for months they will go without eating, but their lean tissue is conserved, they wouldn't last many winters if they didn't do this. Animals in torpor also have high blood BCAAs. So a hypothesis is that the obese are in some kind of torpor-like protein sparing state and it seems eating a diet low in BCAAs (around 8g a day) is enough to switch out of this state.



In the above clip Ray mentions tryptophan, cysteine, and methionine as amino acids that are only needed in extremely low amounts in adults, they are growth amino acids. BCAAs are also critical to growth, its no surprise then that milk has one of the highest BCAA to total protein ratios, ~20%. But perhaps in the obese these amino acids are inhibiting a higher metabolism and weight loss? Fruit is lowest in BCAAs.

This kind of weight loss diet, while not low calorie, is low overall protein, since theres no easy way to eat only low BCAA protein sources. Gelatinous cuts of meat are the best. In the PR rodent experiments, protein is 7% of total caloric intake, higher and the effect drops of quickly.


PR (10%) study in people from exfatloss link

The protein is not even that low when compared to RDA.


PR study in mice from exfatloss link



PR study in mice from exfatloss link

Eat more and move same, results in lost weight and "increased energy expenditure".



PR study in mice from exfatloss link

Interestingly, here added BCAAs lead to extra weight gain.


PR study in mice from exfatloss link. Bottom right graph is "calories out".


High resting metabolic rate is a goal of a bioenergetic approach to health. i.e. how to get maximal energy throughput. Is BCAA acting as a metabolic brake in some susceptible people?

Perhaps its not even genetics that makes people susceptible, but it is triggered by environmental factors like PUFA combined with stress? We might suspect that once someone follows a low BCAA protocol like this and then returns to a lean state, that they wouldn't have to stay on the protocol since the metabolic pattern has been shifted.

I'll be trialling low BCAA myself, both for the weight loss effect, and the increased basal metabolism. The big difference compared with Ray's advice for weight loss is the lowered protein (though he did point to lowering methionine, cystine and tryptophan as a good thing) and dairy in particular, since he seemed to connect high dairy consuming cultures with leanness, but maybe the picture changes if your already broken metabolically? Using egg shell powder for the calcium lost with the reduction in dairy might be a good way to execute this while still keeping to Ray's diet principles.