Thin Rice Eater
It’s a common question. If carbs can make you fat, why were some populations (e.g. Japanese people) thin while eating a high carb diet?
Dr Peter Attia has written a nice post on this: The War on Insulin: How do some cultures stay lean while still consuming high amounts of carbohydrates?
I basically agree with his ideas, although I think there is a few more answers to this question:
The three big reasons
Here are the main reasons why I think populations could stay thin on high carb diets:
- Low to insignificant consumption of refined sugar (fructose). This may stop insulin resistance from developing.
- Eating mainly unrefined starch (e.g. brown rice, root vegetables) that is slow to digest, due to high fiber content etc.
- Traditionally more physical activity then sedentary western population. Compare a Japanese rice farmer (in the field all day) to an American office worker with a car. If you burn more glucose (via physical activity) then less insulin is needed when you eat carbs.
If you avoid sugar (fructose) and refined high GI starch and stay physically active you can probably stay thin and healthy on a high percentage of carbs. Lots of populations have done so.
Three more factors
- Poverty: These traditionally thin populations were on average fairly poor by todays standards, meaning perhaps they could not always afford all the food they would like to eat.
- Food reward / addiction. This may be controversial but I think there is a point to all this food reward talk that’s been going on in the blogosphere. Our processed junk food and candy is carefully designed to artificially make it taste great and be addictive. It also contains a lot of sugar and starch. It’s like cigarettes: The nicotine makes people addicted, thus they smoke a lot and the smoke gives them cancer. Fast food and candy is also addictive, thus people eat more of it and the sugar / starch overdose makes them fat.
- Genetic makeup. Asians do not look like Caucasians or Africans. They have (on average) way less musculature, they have a thinner build. This means that comparisons between the weight of Americans / Europeans and Asians using BMI is misleading, it exaggerates the difference. Asians are often “skinny fat” or even get diabetes at BMI levels that are considered normal for Caucasians (e.g BMI 24).
What do you say?
What do you think about this common question and the possible explanations?
90
I am a Professor of Biochemistry but we all have a lot to learn.
1. The concept of tortuous metabolic pathway is not in the biochemical texts. Both fructose and glucose proceed through separate pathways of glycolysis but converge at the level of the triose-phosphtates so, at that point, they are essentially the same. The difference in metabolism has to do with the relative rates of the different enzymes and depends on a large number of factors. Ethanol does not proceed through this path except possibly under some unusual conditions. Ethanol is oxidized ultimately to acetyl-CoA and goes into the TCA cycle.
2. Reading your comment, though, it hit me that this process is not called detoxification. In fact, the metabolism of alcohol through the dehydrogenates to acetyl-CoA is not called detoxification either. Detoxification of alcohol usually refers to the process at high alcohol ingestion where alcohol is less like a food than like a drug. In this case, it is not oxidized through the normal pathway but rather through the cytochrome P450 system which is completely different from normal metabolism and is considered detoxification but I don't think that fructose ever enters this system.
3. On the specific point you raise though, glucose is the major source of protein glycosylation. This is because, although fructose exists to a greater degree in the open (free aldehyde) form, there is much less fructose in the blood. First, there is more glucose altogether but, remember, your body maintains blood glucose while it clears fructose. I challenged Lustig on this once and he did have an example where fructose was more important than glucose but this is rare.
That's some of the biochemistry that I do have although I admit that I could use more.
RDF
(i answered this in email so forgive possible duplication)
From my perspective, he is making a parody of teaching biochemistry which is my job. A metabolic map is like any map. It tells you where you can go but it doesn't show you the traffic lights or the road construction. Also, what's missing from Lustig's compelling talks is data. The studies that support sugar as toxic are done at a total carbohydrate of 55 %. Under those conditions adding fructose is clearly worse than adding glucose, but is that what we want to know. Science is about the facts and understanding so, in some sense, there are no credentials but Lustig is simply not acting like a biochemist although he wants to take credit for being one. We could be wrong in our methods but he is definitely not a biochemist. The reason real biochemists don't like to jump in here is because we are reluctant to make sweeping statements. But we have some data and as far as we know, the effect of replacing fructose with glucose even under the conditions that he cites, is generally not as great as replacing any carbohydrate with any kind of fat.
The bottom line from a therapeutic perspective is that the mass of data clearly shows that for diabetes and metabolic syndrome and obesity, dietary carbohydrate restriction is the best bet -- if it doesn't work, thou can try something else. If you want to take sugar out of the diet, even just sugared soda as a strategy for reducing total carbohydrate, that may be very effective for obesity. For diabetes, it may be better to reduce starch depending on the individual case and conditions. What's scary about Lustig is that he is on the American Heart Association panels, the group who have gone out of their way to attack low carb diets and to distort the scientific data.
In term of the original thread on Asian diets, it is obvious that we don't know enough to make any clear statements although all the comments touch on relevant stuff. Overall, what we know is less than what we don't know but if you give up on scientific method, you've got nothing.