Leucine & Phenylalanine Enriched YoYo-Diets Ameliorate Fat Gain, Protect Muscle & Maintain T4→T3 Conversion

Too little leucine & phenylalanine in O.'s diet?

Actually it is quite counter-intuitive that the "YoYo"-diets competitive boydbuilders adhere to (diet vs. bulking phase) are capable of producing such amazing physiques. I mean, when Mr. and Mrs. Average "diet down" and "bulk", the result will usually be neither aesthetic nor healthy, right?

A recent study from the University of Sao Paulo does now provide some insights into the important role the high amount of essential amino acids (leucine and phenylalanine, to be precise) in the typical bodybuilding diets may play with respect to its moderating effects on the lean muscle loss and body fat gains of Opra-esque ups and downs in body weight.

Leucine + Phenylalanine + diet and refeed = ???

I guess the details in the headline to this paragraph are not actually detailed enough to get an idea of what Donato Jr. et al did in their latest rodent study, are they? I see. I will still try to stick to the most important facts.

Contrary to the beliefs of many mostly female victims of life-long dieting, never eating to satiety is NOT going to promote a bikini body - quite the contrary (learn more)

Donato and his colleagues fed a group of adult Wistar rats diets that differed only in their amino acid make-up. Both the control and the experimental diet were based on the same synthetic standard chow (remember what you've learned about synthetic chow lately?). What was different, though was the form of protein / amino acids the scientists used to replace 8.55g of the cornstarch (per kg) of the original diet. The final diets did thus contain either...

• 8.55g of casein (control), or
• 5.45g l-leucine + 3.1g l-phenylalanine (LP)

... as replacements for the cornstarch. Since both were still isocaloric and had an identical protein content (12%) this modification would allow Donato et al. to see if the different amino acid profiles would have nay effects on the weight development of the rodents.

I guess by now you may be asking yourself about the connection to Oprah and boydbuilding diets, right? Well, the 28-day experiment actually had 2 phases a dieting and a maintenance phase. Both cycles were 14 days long. In the first one, the rodents dietary intake was cut in half, while they were allowed to eat as much as they wanted (ad-libitum feeding) in the second 14-day cycle.

YoYo or not - is that the question?

Now, what would you guess happened? I mean, remember: Both diets had an absolutely identical amount of calories and protein - so, the rodents in both groups "hit their macros", right? The logical answer - at least to an increasingly popular, but over-simplistic dietary paradigm - must be: "Nothing! Both groups will end up at an identical body composition.", right!? A brief glance at the data in figure 1 does however suffice to tell you the IIFYM prognosis was not exactly correct - at least not if we take the changes in body composition into account.

Figure 1: Effects of weight cycling with casein (control) and leucine + phenylalanine (L+P) on body composition (left), feed efficiency (=how much weight do you gain per gram of food) and weight (Donato Jr. 2013)

So what can we conclude based on the results in figure 1? Firstly, the small figure on the bottom right goes to show you that weight cylcing per se does not make you "heavy" as in "having a higher BMI than somebody who does not weight cycle". The large figure on the left, on the other hand informs us that weight cycling can cost you muscle and make you fatter - 4% fatter to be precise. Skinny fat, so to say. Notwithstanding, the data from the Donato Jr. study does also tell us that the provision of a low amount of additional leucine and phenylalanine minimized the fat gain in the bulking phase and had beneficial effects on amount of lean mass the rodents maintained and build during the 4-week study. The net result is a higher body weight in the L+P group, at an almost identical body composition.

Leucine + phenylalanine also blunt the reduction of T4 → T3 conversion

If we look closer we do yet see another related, but non-negligible advantage: The typical downregulation of the conversion of the "inactive" thyroid hormone T4 to the "active" thyroid hormone T3 in response to long-term dieting was significantly reduced by the provision of leucine and (I will just go on a limb here and say "more importantly") the neurotransmitter precursor phenylalanine.

Figure 2: Effect of weight cycling of markers of glucose and thyroid metabolism (Donato Jr. 2013)

This did yet not translate into a significant amelioration of the highly significant (>50%) deterioration of the blood glucose metabolism, and the triglyceride levels (not shown) were actually 20% lower in the casein yoyo group (CON) than in the non-weight cycled control group. From a health perspective, the addition of leucine and phenylalanine is thus "only" useful, because it will help you retain or actually build muscle mass (with the data we have, it's difficult to say which effect was the dominant one, but I'd suspect it's the anti-cabatolic one).

Bottom line: You need to be careful about mis- and over-interpreting the results of the study at hand - and that's not just because it's "only a rodent study".

If there was one "take home message" from the study at hand, I guess it would be very similar to the one from the one of the December 2012 post I borrowed this figure from: "Make sure to get at least 10g of EAA with each of your meals"... ah well, "... and avoid 'classic' YoYo dieting à la Oprah, whenever possible - of course!" ;-)

The alleged "lean mass gains" on the L+P diet come at the expense of a non-negligible increase in body fat. Overall the lean mass to fat mass ratio is thus not better than in the continuously fed rodents. And unless your beauty ideal is all about being "massive", this is not necessarily going to be an improvement to your physique.

If you take another look at figure 1 you will also see that the feed efficiency, i.e. the amount of weight you gain per kcal you consume was not reduced but increased by the addition of leucine and phenylalanine. This may be a result of the pro-insulinogenic and "anabolic" (Nuttall. 2006; Iverson. 2013), as well as the anti-cabatbolic effects of these amino acids and is thus not necessarily "bad".

It would nevertheless be highly unwarranted to believe that supplementing your diet with leucine + phenylalanine on a a "lean bulk" would yield significant advantages - this hypothesis is clearly not supported by the study at hand. The same goes for the usefulness of supplementing isolated amino acids, in this case leucine and phenylalanine, on top of a high protein diet, in general. In fact, I can refer you directly to an older article of mine that confirms that you better make sure to get the full dose of 20g+ of whole protein than trying to make up for it by adding additional aminos (learn more)

References:

• Donato, J. et al. Effects of leucine and phenylalanine supplementation during intermittent periods of food restrictionand refeeding in adult rats. Life Sciences. 2007 [epub ahead of print]
• Iverson JF, Gannon MC, Nuttall FQ. Ingestion of leucine + phenylalanine with glucose produces an additive effect on serum insulin but less than additive effect on plasma glucose. J Amino Acids.
• Nuttall FQ, Schweim KJ, Gannon MC. Effect of orally administered phenylalanine with and without glucose on insulin, glucagon and glucose concentrations. Horm Metab Res. 2006 Aug;38(8):518-23.