Histidine As a Fat Loss Adjuvant? 6% Fat Loss Without Dietary or Exercise Intervention & More Than Half a Dozen Other Reasons Not To Ignore This Essential Amino Acid

Histidine as a fat loss adjuvant? Laughable? Not for the obese! For lean folks like her? We'll see...
If I had to guesstimate the number of fitness enthusiasts who have ever heard of histidine at all, I would say that 50% probably don't even know what it is, while the majority of the lightened ones will re-iterate what the supplement business has been preaching them "You get more than enough histidine, anyway. So don't worry our superior beta-alanine supplement will work even if you don't take additional histidine."

Short term studies confirm this notion. It looks as if we usually have more than enough histidine to have it recombine with beta alanine and form carnosine, but long-term studies are missing and let's be honest: How likely is it that an essential amino acid is nothing but a servant to a non-essential amino acid from the 2nd row?

Early results: Histidine modulates feed efficiency

Actually we could have known that histidine could have some merit as a standalone supplement for more than 50 years now, so I am not sure if the recent publications of two studies by Feng et al. in Diabetolgy and Kumi Kimura et al. in Diabetes, the journal of the American Diabetes Association are going to change that over night. What is certain, though, is that they clearly support findings that date way back into early mid 20th century, when Ellison & King found that the provision of a low histidine diet to rodents increased the feed efficiency (=weight gain per energy unit) by 75%, while the addition of 0.75% histidine (per kg chow) to an already histidine sufficient diet  (Ellison. 1968) led to a 30% decrease in food efficiency.

About 45 years later, the previously mentioned studies on the effects of histidine on hepatic gluconeogenesis (Kimura. 2013) and insulin resistance (Feng. 2013) in rodents and human volunteers, respectively, could bring the hitherto often depreciated histamine precursor back to the center of scientific attention.

4g/day histidine improve insulin restiance, reduce fat mass and suppress inflammation

In that, the study by Feng et al., which investigated the effect of 4g/day supplemental histidine on the degree of insulin resistance, inflammation, oxidative stress and metabolic disorders in 100 obese women with the metabolic syndrome (aged 33–51 years; BMI≥28 kg/m²), is probably of greater significance for the average physical culturist that the nevertheless enlightening rodent trial by Kimura et al. we are going to address later.
Figure 1: Changes in amino acid levels, glucose & lipid metabolism, body composition and markers of inflammation after 12 weeks on placebo or 4g/histidine per day (Feng. 2013)
The effects the 4g/day of histidine had especially on the markers of inflammation are quire impressive for an amino acid of which you probably thought as either the "abundant" essential amino acid that's only an adjutant to 100% non-essential and on it's own just about as useless carnosine precursor beta alanine or - even worse - as the nasty precursor to the "allergy inducing", "inflammatory" organic nitrogen compound histamine.

"Hold on, but histidine is an allergy causing nasty bitch, isn't it?"

While the former perspective on histidine is laughable anyway, the fact that there were no increases in histamine levels and none of the participants experienced side effects such as headaches, which have been observed in previous trials with whopping amounts of 64g(!) of histidine per day (Geliebter. 1994) as they have been used, when scientists still believed that the main mechanism of histidine on body weight modulation was mediated by appetite reduction, are probably relevant. After all, histamine does play a role in the inflammatory response system of your body that the latter is not negatively, but positively affected by the consumption of pretty high amounts of histidine, is thus an important and in a way counterintuitive observation. On the other hand,
First the glucose repartitioning effects of isoleucine (learn more), now the benefits of histidine - what other secrets are still out there in the world of amino acids?
[h]istidine is a free radical scavenger and can chelate divalent metal ions (Babizhayev. 1994; Lee. 1999). Its effects against oxidative stress have been well investigated in animals and cells. Histidine has beneficial effects on liver and lung injury in rats and has been reported to protect against diabetic complications in a mouse model of diabetes through its actions against oxidative stress (Lee. 2005; Cuzzocrea. 2007; Yan. 2009). It can restrict accumulation of free radicals and delay activation of extracellular signal-regulated kinase and c-jun N terminal kinase in neuronal cells (Kulebyakin. 2012).
Against that background it is actually not surprising that the levels of TNF-α, IL-6 and c-reactive protein (CRP) dropped by 33%, 35% and 33% in the course of the 12 week study period.

Health and weight loss, two independent pairs of shoes?

If histidine is a metal chelator, do I have to be afraid of losing zinc? That's easy to answer and the answer is no and not just because I believe that the importance of zinc is way overrated (cf. "15mg of Zinc are plenty"). Schechter & Prakesh have shown in 1979, already that the ingestion of 4g of histidine on a daily basis influences the excretion of zinc only in the very short run. After 2 weeks the body achieves a new steady state and the zinc excretion returns to normal. What? No you did not pee out all the zinc before. In fact histidine increases the absorption of dietary zinc as well (cf. Freeman. 1977).
Moreover the changes in serum histidine were correlated with the changes in HOMA-IR, NEFA, TNF-α, SOD, GSH-Px, WC, FM and BMI even after further adjustment for age and serum histidine, protein intake, physical activity, alcohol use, current smoking and menopause at baseline.
"Thus, improved insulin sensitivity and alleviation of inflammation and oxidative stress could be due to the increased serum histidine." (Feng. 2013)
What's questionable, though, is how interrelated the modest, but statistically significant weight, or rather fat loss (-6% total fat mass) and the improvements in inflammation are. If we take a peek at the aformentioned rodent study by Kimura et al. who observed that the effects of histidine are mediated mainly centrally via histamine action on the H1 receptors in the brain, which will - independently of insulin (!) - downregulate the hepatic glucose production, it becomes more and more evident that non-obese / insulin-resistant individuals for whom an abundant hepatic glucose production hardly ever is a problem are less likely to benefit than the patients with type 2 diabetes, Kimura et al. implicate as the group that would be most likely to benefit from high histidine diets.

What else do we know about l-histidine?

In the end, we are thus back to square one. But maybe we can find other arguments in favor or against keeping an eye on adequate histidine intake that would be significant for the non-diabetic majority(!?) of the SuppVersity readers, as well. Let's see, what about
  • Ok, put up or shut up - where is the relation between histidine, histamine and obesity? As so often I have to say in advance that the intricacies of the role the histamine receptors in the brain play in the regulation of food intake and metabolism are not yet fully understood. What we do know is that histidine is the dietary precursor for histamine and that the latter can interact with the same receptors (H1-H3) which participate in the regulation of dopamine, serotonin, and norepinephrine release and exert direct modulatory effects on food intake, meal frequency, adiposity and thermogenesis (Masaki. 2003; Masaki. 2004; Yoshimoto. 2006; Yoshimatsu. 2008).
    improved absorption of vitamin B12 and increased liver folate levels (Williams. 1976) 
  • low histidine intake increases carnosine breakdown, so that the ant-inflammatory intra-cellular buffer carnosine you are trying to increase by taking BA would decrease to be used as a histidine source if you actually got too little histidine in your diet (Tamaki. 1984)
  • increased absorption and excretion of zinc, with a primer on the former, when intakes are low, so that the overall result is an improved management of zinc (Sandström. 1985; Van Wouwe. 1989) 
  • potential anti-Alzheimer's effects; if we simply assume that an increased amount of dietary histidine could ameliorate the histidine and histamine reductions in the brains of Alzheimer patients (Mazurkiewicz-Kwilecki. 1989), it would be logical to assume that the presence of this metal-chelator could prevent the accumulation of toxic levels of copper in the brain
  • significant increases in UCP-1 activity (+57%) in brown adipose tissue and thus higher energy expenditure, reduced appetite, significantly lower feed efficiency (-30%), reduced insulin levels (-48%) and significantly lowered visceral fat pad weights; allegedly in rodents w/ additional 5% histidine in the diet (Kasaoka. 2004) 
Now you could certainly argue that the studies which support the weight loss effects Feng et al. observed in their obese subjects were almost exclusively conducted on rodents... what am I supposed to say? You're right and you know that I am very skeptical that UCP-1 and brown adipose tissue activity play a significant role in human weight / body fat control. Still, the high correlations between the histidine / total protein ratio Okubo et al. observed in a cohort of non-obese 18y-old female Japanese students does clearly suggest that at least part of the effects are not species specific (Okubo. 2005).

Additional health effects 
Milk thistle is unquestionably the more prominent liver protectant (learn more)
Furthermore, histidine also prevented colitis by reducing gastric inflammation (Andou. 2009) and exerted  ameliorative effects on
  • LDL oxidation and glycation (Lee. 2005), 
  • alcohol induced liver failure (Liu. 2008), 
  • acetaminophen induced liver injury (Yan. 2009), 
  • diet induced hepatic steatosis (Mong. 2011)
when it was co-administered with carnosine. Unfortunately, none of the studies tested, whether the same results would have been observed if only one of the compounds had been used in the respective rodent trials.

So, no strings attached? Well, not exactly...

As usually the dose-response curve is yet non-linear and an exuberantly high intake of histidine (8% of the diet in rodents → far more than 70g per day for humans) can lead to copper depletion and corresponding lipid disturbances in cholesterol metabolism (Harvey. 1981). Needless to say that for people with a messed up histamine metabolism far lower doses could potentially exert negative effects. It should be mentioned though that the equation"more histidine = more histamine" does not necessary hold - just take a look at the data from the Feng study: More histamine? Yes! Beneficial effects? Yes! Increased circulating histamine? No!

Bottom line: Wile it appears likely that the provision of supplemental histidine in amounts of up to 4g/day could provide a highly beneficial adjunct to exercise and diet intervention in obese and/or diabetic individuals, it remains to be seen, whether or not lean, healthy and insulin sensitive fitness enthusiasts benefit to a similar degree.

Histidine content of various foods; w/ a focus on high histidine food items
While I would exclude that the profound anti-inflammatory effects Feng et al. observed could hamper your performance / gains, I would not exclude that the non-vegetarian majority of the SuppVersity readers is not exactly at risk of running out of histidine anytime soon (see table on the right for good dietary sources). Against that background, you may have to revise your perspective on this rarely talked about amino acid. What you probably don't have to do, though, is to go and buy a pouch of l-histidine to up your histidine intake to exorbitantly high levels... well, at least not until research on human beings confirms the beneficial effects on UCP-1, insulin and the body fat levels Ksaoka et al. observed in non-obese rodents.

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