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Vitamin C and Low-Carb diets

A former guest Mike Sweeney RD, had an interesting recent interview on a Keto podcast: The claim is at timestamp 46:20. It was interesting to hear a registered dietitian with such *ahem* different views, but I wanted to focus on one particularly interesting claim which I have dug into myself because I previously heard the same claim within the last year. You can listen above for his exact words but the basic claim is this: "Those on low carb diets require less vitamin C than those on high carb diets. This is because Vitamin C and Glucose have a shared transporter (GLUT#). The more carbohydrate in the diet, the more glucose, the more glucose, the higher the vitamin C requirement as they compete for the same transporter. On low-carb, there is less glucose, thus less competition for the transporter, thus a lower Vitamin C requirement." I have heard that this means the RDA for Vitamin C is "irrelevant" and "doesn't apply" to low carb dieters ..... I see a couple of significant problems: (1) Competition for the transporter would only be relevant if either Vitamin C or Glucose were sufficiently high in those areas where the transporters do their job. I believe in the case of hyperglycaemia, there can be an issue with Vitamin C uptake. But where is the evidence that high carbohydrate diets, of themselves result in sufficiently high levels of glucose to make competition for these transporter an issue that would affect Vitamin C requirements? (2) Why would cell requirements for Vitamin C be lower? Rummaging in "Nutrient Metabolism: Structures, Functions and Genes" (Martin Kohlmeier), carbohydrate metabolism does not seem to require Vitamin C. Maybe he is saying that although cell Vitamin C requirements are the same, because of high glucose levels, more vitamin C is needed to outcompete the glucose and reach the cells? It all sounds pretty sketchy so would love to hear you guys take it apart.

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