Fruit and vegetables, last post (almost)

I've posted twice on the links between fruit and vegetables and oxidative damage to lipids, protein and DNA. This then begs the question as to why diets high in fruit and vegetables, on an epidemiological basis, are associated with less chronic diseases than diets deficient in fruit and vegetables. There seems to be a paradox here, fruit and veggies are repeatedly associated with oxidative damage, avoiding them is repeatedly beneficial, yet overall they look good for health when studied at the population level.

So, epidemiology finds fruit and veg are associated with better health. They shouldn't be. But epidemiology shows only shows association, never causality. Only interventions studies do that. On the basis of controlled intervention studies fruit and vegetable consumption shouldn't improve health, so there must be confounding factors here.

You have to ask what the confounding factors might be. Is there anything about the sort of person who eats lots of fruit and veg, compared to those who don't, which might over ride the damage done by the vegetables?

Well, some factors come to mind.

Poverty has to be the first. Poor people do worst on a health basis on just about every measurement possible. They also don't buy much in the way of vegetables. I remember one study showing that poverty is associated with very poor outcomes in diabetes. The conclusion was that we should spend lots of money educating poor people to spend their limited resources on vegetables. You can guess what I think about that. The obvious solution is to give MONEY to those in poverty. When they are rich enough, their health might improve. They might even be able to tolerate eating vegetables with impunity. Of course the link between poverty and ill health is epidemiological. I haven't seen an intervention trial where a large group of impoverished people were give £100,000 each per year and the placebo group given a similar notional value in Enron shares. I'm waiting for that one.

The second consideration is to ask what vegetables might displace from the diet. That is, what do people eat instead of vegetables. Chances are it is sugar or high fructose corn syrup that forms a big chunk. In the fruit and vegetable wash out study a typical daily diet is given. The diet, including total calories, was very strictly controlled. The depletion diet was high in carbohydrate, but mostly from potatoes, rye bread and white bread. The only fructose in the menu was from sucrose in carrots (which are loaded) and in the cake. So this is a pretty low sucrose diet. Eating sucrose and high fructose corn syrup is like getting all the bad aspects of fruit and vegetables but none of the vitamins needed to process the sugars.

Vegetables are bad, but refined sugar is probably worse.

It is possible.

Peter