Whirrly--This is the first "paper" mentioned in that video, a letter to the editor about a meta-study the authors did looking at flow-mediated dilation and low carb vs. other diets. I have no idea what criteria a letter to the editor might go through to be published--I'm pretty sure it will be nothing like what would be required to be considered peer-reviewed literature.
This letter lists all of ten references--one to the study the letter was in reference to.
That's reference one. Reference two is about flow mediated dilation, but not specifically about low carb--and it's a cohort study, so even if there was a "low carb" arm somewhere in there, it won't be people on low carb diets, but people who happen to be eating the least carbohydrate--basically, people eating higher fat, higher protein diets without cutting the carbs.
Reference three is actually low carb. A search for the word "artery" gave me nothing, as did "flow." Couldn't find anything related to blood flow.
Reference four compares flow mediated dilation with a low carb vs. a mediterranean diet. There was a difference between the two in the mediterranean diet's favour at day five, but it disappeared at day 60
In reference five--switching between olive oil and carbohydrate for part of the diet's calories made no difference to flow mediated dilation. This is sort of run of the mill, where fat does decrease flow mediated dilation, saturated fat like palmitic acid in butter and cream seems to be the "villain."
Reference six is actually relevant, so let's skip that for now.
Seven--this one compares a high fat to a low fat diet, not low carb to low fat. Maybe it matters to somebody, just not to me.
Eight--yay, team. This is a Volek study.
After 12 weeks, peak flow-mediated dilation at 3 hours increased from 5.1% to 6.5% in the CRD group and decreased from 7.9% to 5.2% in the LFD group (P = .004). These findings show that a 12-week low-carbohydrate diet improves postprandial vascular function more than a LFD in individuals with atherogenic dyslipidemia.
Going back, the study in reference six was similar in that it did compare flow mediated dilation on a genuinely low carb diet (Atkins, under 20 grams of carbohydrate) and a low fat diet. There was an improvement in flow mediated dilation with low fat vs. low carb there. The authors mention a weakness of their study;
There are several limitations of this study. First, unlike other studies,14,28 we eliminated risk factors to focus our analysis of dietary effects on vascular function, thereby making it difficult to generalize these findings to all of the obese patients who typically have other risk factors.
In other words, people were screened out if they had hypertriglyceridemia, high insulin levels etc. Volek's group was described as having moderate hypertriglyceridemia, we're probably looking at one study where people were relatively insulin sensitive vs another (Volek's) where they were less insulin sensitive, if you're looking at the effects of blood fats on flow mediated dilation, this is an important thing to consider.
Nine is a year long intervention with people randomized to low carb or low fat. Low fat does better, at least that's what the abstract says... How many people, randomized to a diet for a study, are all that faithful to the diet by the end of the year? The general history of diet studies says "not many." At this point, it's possible people have remembered how much they love bacon and butter--but forgotten the important parts of the low carb diet, such as not eating carbs.
Ten is a meta-analysis of observational studies. Which is to say, people who just happened to eat less carbohydrate than their peers were lumped together, simply eating more of your calories as fat would give you a high "low carb score." Piffle.
One thing that can't be shown in any of this--where there is a difference in flow mediated dilation, should we care? Flow mediated dilation is in response to a stressor. Pressure is used to compromise blood flow, the body responds, when given the option, with vasodilation. As with any response to stress, the strength of the response scales to some degree to the insult received. This may be me saying something ridiculous--but it's always possible that under one diet, restricting blood flow might be more stressful, the oxygen deficit etc., might be greater over the given time period than under the other diet. All things being equal, greater flow mediated dilation might be better than lesser, but still, conditions besides the constriction itself might go into deciding just how much dilation is even appropriate.