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Carb-loading and your heart, you may want to put the pasta down…

carb loading cat

So if you are one of the bodybuilders, powerlifters, marathon runners, or just people who like to binge-eat every now and then — no judgment all you can eat pizza day is a thing I’m told telling myself — there is some bad news. If you like to preload carbs like they are the magic bullet to your workout woes, you may want to rethink it because according to a new study, it can have an acute and detrimental effect on heart function.

A group of researchers — who may or may not enjoy the movie pumping iron, I’m plugging a lot of movies lately aren’t I? —  studied 33 individuals who were given an acute carbohydrate load in the form of a 264-kilocalorie shake. If you’re super curious — I know I was — there are 4-Kcal per gram of carbohydrate, so if we assume the entire shake was carb based, there are about 66 grams of carbs.

Although, to be honest, I’m not sure how you would be able to stomach a just carb shake unless it was mainly common sugars but then why call it a carbohydrate shake at that point? Since I cannot see the full study I don’t actually know what was used (curse you, useless paywalls!!!) so just go with it, you know… for science.

They then recorded the subjects’ blood levels for six hours looking for a number of things, largely it was whether this “acute metabolic challenge” could alter the heart’s production of atrial natriuretic peptide (ANP). ANP is a hormone that helps the body get rid of excess salt and reduces blood pressure, but more importantly (in my opinion anyway), it helps protect the heart from enlargement.

Moreover, from previous research, it has been shown that obese people make less ANP, predisposing them to salt retention and hypertension. So if a high dietary carbohydrate load has the ability to suppress circulating ANP concentrations, this would be a disadvantage to obese individuals who have lower ANP levels to start, particularly for the heart.

To eliminate that funny thing called variability in diet, the participants were “normalized” on a standard diet for a couple of days to remove any background dietary variability, prior to the study actually starting. Surprisingly, especially as someone who personally carb loads prior to powerlifting,  the researchers found that drinking the high-carb shake led to a 25 percent reduction in ANP in participants over the course of several hours.

“The carbohydrate load had a significant and notable effect on circulating ANP levels. Experimental studies suggest that it’s not good to make less ANP,” said senior author Thomas Wang, M.D., adding that “carb loading” may not be ideal for the body.

The investigators also looked at the mechanism for the decrease in ANP levels. They were able to reproduce the findings in mice and found that the principal driver for the acute reduction in ANP appeared to be the increase in glucose.

“When you take in a high-carb shake a lot of things happen, including increases in glucose and insulin. However, the increase in glucose appears to be the main thing driving the drop in NP levels,” Wang said.

This novel mechanism involved a molecule known as miR-425, which the research group has previously described as an inhibitor of ANP production. As it turns out, the glucose — which is made from the breakdown of carbs — causes the cells to make more miR-425, and that, in turn, causes a reduction in ANP.

You would also assume that this would cause a spike in blood sugar, which could also lead to other health issues not involving the heart itself.

But — and this is a big but — since the study did not actually look at preloading carbs prior to a workout (or post workout for that matter if that is your thing) it is hard to say for sure what the effects to the heart would be. Exercise should help offset the insulin spike brought on by the carbs, but then again if miR-425 is released in the presence of higher glucose, it may not actually change the overall outcome.

Given the study, I might just try to cut back on the carb loading, but then again I’ve been doing it for 10 or so years now, so it might just be a case of what is done is done. I haven’t been this confused about working out since I got that shake weight for Christmas…

Sources:
Arora, P., Wu, C., Hamid, T., Arora, G., Agha, O., Allen, K., Tainsh, R., Hu, D., Ryan, R., Domian, I., Buys, E., Bloch, D., Prabhu, S., Bloch, K., Newton-Cheh, C., & Wang, T. (2016). Acute Metabolic Influences on the Natriuretic Peptide System in Humans Journal of the American College of Cardiology, 67 (7), 804-812 DOI: 10.1016/j.jacc.2015.11.049

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