In spite of the fact that its development is most strongly linked to the consumption of a generally unhealthy, energetically dense diet, there are several lines of evidence which suggest that the ingestion of exorbitant amounts of fast-digesting fructose from high fructose corn syrup (HFCS) sweetened beverages or processed foods is one, if not the most reliable motor of its development (Volynets. 2012).
On a molecular level fructose has been shown to trigger the production of fat from glucose in the liver (de novo lipogenesis | DNL). It does so by activating certain enzymes via the sterol regulatory element binding protein-1c (SREBP1c) and/or the carbohydrate-responsive element-binding protein (ChREBP). In conjunction with the corollary hepatic oxidative stress and the subsequent increase in insulin resistance, the onslaught of readily absorbed fructose from processed foods and HFCS-sweetened beverages is thus like gasoline on the fire of the obesogenic baseline diet some people refer to as the "standard american diet" (learn why the "SAD-diet" is so good at making you fat). On the whole, however, the accumulation of fatty streaks in the liver that's so characteristic of NAFLD is yet only the point of departure of the journey to the land of the super-obese type II diabetics.
Now this journey from slightly overweight to super-obese is a journey of which many previous studies studies already suggested that it could take a very different route if people consumed higher amounts of protein and/or certain amino acids (AAs):
- Theytaz et al. (2012), for example, found a "liver cleansing" increase in VLDL-TG release by the liver with an essential AA-enriched diet, and
- Bortolotti et al. (2012) showed that a protein-enriched diet can effectively reduce the fructose induced lipid accumulation in the liver through increased energy expenditure.
Where's the control group? Previous studies show that diets which are supplemented with NEAAs (alanine, glycine, proline, aspartate, histidine, and serine) or citrulline have metabolic and nutritional effects similar to a regular control diet, alone (Osowska. 2006; Jegatheesan. 2015). The CNEAA group is thus the "control" group in the study at hand. That's "ok" and doesn't make the study results useless, but in view of the fact that the data in Figure 2 shows more than just an ameliorative effect of citrulline on NAFLD, I would have preferred a regular control group in which the rodents had been fed standard chow without added non-essential amino acids.To confirm or falsify their hypotheses, the researchers randomized twenty-two rats into four groups on different diets:
- CNEAA as in control - control diet without added fructose + 1g/kg non-essential amino acids (for humans that's roughly 11g per day | this was the control diet in the study at hand)
- F as in fructose- control diet enriched with 60% fructose without supplements
- FNEAA as in control + fructose - fructose enriched diet (F) + 1g/kg non-essential amino acids (which happens to be the control diet in the study at hand)
- FCIT as in fructose + citrulline - fructose enriched diet (F) + 1g/kg citrulline
|Figure 1: Relative changes in liver weight, hepatic triglyceride content as well as the liver markers AST, ALT and ALP a marker of kidney health compared the "control" group (CNEAA | Jegatheesan. 2015)|
|Figure 2: Both FNEAA and FCit rodents had a better body composition than the rodents on the NEAA supplemented control diet, but the differences reached statistical sign. only compared to the fructose (F) group (Jegatheesan. 2015)|
So, why would you even consider citrulline, if the NEAA combo is better for your liver?
Well, the reason that the average physique enthusiast, may still choose citrulline as his "fructose buffer" of choice is easy: Firstly, the differences in terms of liver health are not really statistically significant. Secondly and more importantly, though, citrulline triggered a reduction in visceral and total fat mass and a relative increase lean mass that was not observed in the NEAA group. And let's be honest: Isn't this type of body recompositioning effect what many of you are striving for?
What is most astonishing though, is that you could have these fat loss and muscle gain effects not just despite, but maybe even because you're guzzling HFCS drinks all day (obviously we'd have to have a citrulline + baseline diet group to confirm that). If we assume that the results translate 1:1 to human beings, the one thing you had just ~10g of citrulline per day. Is this possible? Well, it is, but let's be honest with ourselves: The inter-group differences between the control and the citrulline + fructose were not statistically significant. So while there were improvements those were not pronounced enough to be of statistical significance even in rodents. It is thus not really surprising that you haven't heard of citrulline as the "get jacked" amino acid very often... even though, evidence that it can help you to get jacked does exist (more).
- Bortolotti, Murielle, et al. "Effects of dietary protein on lipid metabolism in high fructose fed humans." Clinical Nutrition 31.2 (2012): 238-245.
- Jegatheesan, Prasanthi, et al. "Effect of specific amino acids on hepatic lipid metabolism in fructose-induced non-alcoholic fatty liver disease." Clinical Nutrition (2015).
- Jegatheesan, Prasanthi, et al. "Citrulline and Nonessential Amino Acids Prevent Fructose-Induced Nonalcoholic Fatty Liver Disease in Rats." The Journal of Nutrition (2015): jn218982.
- Marchesini, Giulio, et al. "Nonalcoholic fatty liver disease a feature of the metabolic syndrome." Diabetes 50.8 (2001): 1844-1850.
- Osowska, Sylwia, et al. "Citrulline modulates muscle protein metabolism in old malnourished rats." American Journal of Physiology-Endocrinology and Metabolism 291.3 (2006): E582-E586.
- Theytaz, Fanny, et al. "Effects of supplementation with essential amino acids on intrahepatic lipid concentrations during fructose overfeeding in humans." The American journal of clinical nutrition 96.5 (2012): 1008-1016.
- Volynets, Valentina, et al. "Nutrition, intestinal permeability, and blood ethanol levels are altered in patients with nonalcoholic fatty liver disease (NAFLD)." Digestive diseases and sciences 57.7 (2012): 1932-1941.