It’s only a very short segment, but it’s a crucial pillar in The Game Changers movie’s argument that a vegan diet is optimal for health and athletic performance.
The narrative goes something like this: Animal foods impair endothelial (blood vessel lining) function and blood flow; plant foods improve endothelial function and blood flow; therefore, vegan diets are better for health and athletic performance than omnivorous diets.
There’s no question that endothelial function and blood flow are important factors in health and athletic performance. But the evidence cited in the movie doesn’t support the overarching vegan diet narrative.
The segment begins with a, frankly, ridiculous “experiment”, conducted by Dr. Robert Vogel on three Miami Dolphins players. It apparently shows that eating a meat burrito increases the amount of fat in their blood compared to eating a bean burrito. And that this translates to impaired blood flow and impaired athletic performance (neither of which is tested). It’s entertaining, but not scientific. Not even close. So, we should ignore it.
A total of 24 peer-reviewed studies are then cited in support of the “experiment”, while James Wilkes, the narrator, makes three statements:
- “Dr. Vogel’s experiment is backed up by numerous studies measuring how a single animal-based meal can impair blood flow.”
- “I also found a large body of research showing that plants have the opposite effect, improving endothelial function and increasing blood flow.”
- “Controlled studies show that simply drinking beet juice before training allows subjects to cycle 22% longer and bench press 19% more total weight.”
Let’s take each of these statements in turn and have a closer look at the cited studies in the context of the broader claims made by the movie.
A single animal-based meal can impair blood flow
The first is not a controlled trial, so we can discount it.
The second is a controlled trial comparing a high-fat meal (including animal foods) with a low-fat meal (including no animal foods). The high-fat meal did appear to increase triglycerides (fat) in the blood, increase oxidative stress, and impair endothelial function two hours later, while the low-fat meal did not. However, the subjects were not randomised into the high-fat and low-fat groups (at least the paper doesn’t mention it), so we should be cautious about the results.
The third study is perhaps the most interesting. It was a (small) randomised crossover trial comparing eating a hamburger patty (on its own) with eating a hamburger patty plus avocado. The meat alone seemed to increase blood triglycerides, increase inflammation, and impair endothelial function soon after the meal. When the avocado was added, triglycerides were still increased (but no more than with the meat alone), but there was no inflammation or endothelial dysfunction.
There is very little evidence of anything here. At a push, there may be some suggestion that eating animal foods increases triglycerides (fat) in the blood shortly after a meal (entirely expected as the fat from the meal is transported to the working tissues of the body) and may temporarily impair endothelial function and raise inflammatory markers. However, the latter two effects appear to be completely offset by eating plant foods alongside the animal foods. It certainly doesn’t tell us anything about the effects of eating only plant foods. If anything, it tells that an omnivorous diet doesn’t seem to cause any problems.
Plants improve endothelial function and increase blood flow
Twenty studies were cited here. They all looked at the effects of consuming plant foods high in polyphenols and flavonoids on endothelial function. Your time is precious, so let’s just look at the three most recent (4, 5, 6).
These were all well-designed, randomised, double-blind, placebo-controlled trials. The first compared the effects of twice daily blueberry smoothies versus placebo for six weeks in 44 adults with metabolic syndrome. The second compared the effects of four times daily blackcurrant juice drinks versus placebo for six weeks in 66 healthy adults with low fruit and vegetable intake. And the third compared different doses of blueberry in a single drink versus placebo in 21 healthy men.
The results were consistent. The blueberry and blackcurrant drinks improved endothelial function compared to the placebo drinks. (Other studies showed similar results with different polyphenol-rich plant foods.) So, The Game Changers is right. Consuming plant foods high in polyphenols improves endothelial function.
But here’s the wrinkle. The subjects in these studies weren’t vegans. There was no selection criteria excluding meat eaters. So, we can assume that the vast majority of subjects were omnivores (mirroring the proportions in the general population). This evidence, then, tells us that including polyphenol-rich plant foods in an omnivorous diet is likely to be beneficial to endothelial function. It doesn’t support the narrative that the only way to achieve vascular health is to eat only plant foods.
Beetroot juice improves athletic performance
The one study cited here was a review of randomised controlled trials testing the effects of beetroot juice on intermittent high-intensity exercise in various athletic disciplines (7).
Overall, the results suggest that consuming beetroot juice, in a single dose or for several days, may improve certain aspects of athletic performance. The movie plucked two of the biggest percentage improvements (22% and 19%) from two individual studies, giving us a far more favourable picture than that given by the authors of the review paper. And, again, the subjects were not vegans. As with the polyphenol studies, we can assume they were mostly omnivores. So, the evidence indicates that beetroot juice may improve some aspects of intermittent high-intensity exercise performance in the context of an omnivorous diet. Not that vegan diets are superior to omnivorous diets for athletic performance, as the movie narrative would have us believe.
It may be possible that, as The Game Changers suggests, a vegan diet can improve endothelial function, and, therefore, athletic performance and health compared to an omnivorous diet. But the current scientific evidence – even the studies cherry-picked by the producers of the movie – doesn’t support that hypothesis.