The Benefits and Risks of Carnitine Supplements

Our TMAO levels appear to increase as we age, perhaps due to an increase in the relative abundance of TMAO-producing species of bacteria in the guts of the elderly. Perhaps this rise in TMAO is responsible for some age-related ailments. For example, studies have found those with elevated TMAO levels have twice the odds of frailty and an increased risk of hip fracture. Water-only fasting can cut TMAO levels nearly in half within 24 hours, though the levels surge right back up after returning to the same diet that increased them in the first place. The researchers conclude this dip “may decrease the chance of Coronary Artery Disease development for at least the duration of fasting,” but fasting has to be among the most unsustainable of dietary patterns, in fact guaranteed to kill you if you keep it up long enough. Instead of cutting everything out of your diet, how about just the foods concentrated with the TMAO precursors, carnitine and choline. In other words, as one endocrinology journal editorial put it, maybe TMAO should instead stand for Time to Minimize intake of Animal products.”

Feed a vegan a steak and they don’t get the bump because they haven’t been fostering those steak eating TMAO-producing bugs. In fact, even if you give vegetarians and vegans the equivalent of a 20 ounce steak every day for a month, or even for 2 to 3 months, only about half start ramping up production, showing how far their gut flora had changed. But it’s not all or nothing. As I explored before, even just swapping out two servings a day of regular meat for plant-based meat can lower TMAO levels within a matter of weeks.

Even relatively choline-rich plant foods don’t seem to cause a problem. For example, two ounces of pistachios every day actually seemed to cause a reduction in TMAO levels. Same thing with brussels sprouts, the vegetable highest in choline. Researchers had people eat two cups a day for three weeks and their TMAO levels went down as well.

It may be the fiber, which lowers TMAO levels (in mice at least). Or it may be the polyphenols. While eggs and beef make TMAO go up within hours of consumption, those randomized to the fruit group actually saw their TMAO levels go down. Polyphenols can act as prebiotics to some bacteria, but can be bacteriostatic (growth stopping) to others, so polyphenols may “represent a strategy for microbiome remodeling.” For example, a grape pomace extract was able cut TMAO levels by more than half. The effect is unpredictable, though.

Daily ounces of cocoa or cups of green tea didn’t appear to make a difference. While Korean black raspberries significantly lowered TMAO levels compared to placebo at a dose of about an ounce of freeze-dried fruit a day for a month, those randomized to 2 cups a day of frozen red raspberries suffered an increase. So-many different types of bacteria have the capacity to make trimethylamine that it’s hard to selectively feed the good ones. Better, then, to prevent the bloom of these bad bacteria in the first place.

Carnitine supplements can also bump TMAO as much as tenfold, so that’s the dark side of carnitine supplements, what might be the bright? In 2007 a randomized double-blind placebo-controlled trial was published of carnitine supplementation for centenarians that found improvements in cognitive function and a reduction in fatigue. This may be an outlier, since meta-analyses of studies of carnitine for cognition and fatigue have failed to show such benefits. Early studies had suggested a beneficial effect on dementia, but later, larger, better studies have sadly not supported the early findings. Still, no other studies had ever looked specifically at centenarians.

For those who want to try carnitine supplements, it still makes sense to eat healthier, since even after months of carnitine supplementation, those eating meat free still churn out less. The same was found for choline supplementation. Within four months of stopping carnitine supplements, TMAO should drop back to baseline.