April 07, 2009
High Fat Protein Diet Causes Metabolic Syndrome?
A diet high in fat and branched chain amino acids (BCAA) causes rats to develop insulin resistance.
It's basically a given that diets loaded with fat can lead to considerable health problems. But a new study in the April issue of Cell Metabolism, a Cell Press publication, shows that in some cases diets that are high in both fat and protein can be even worse.
The researchers led by Christopher Newgard of Duke Medical Center report that rats fed high-fat (HF) diets supplemented with extra so-called branched chain amino acids (BCAA) don't have to eat as much or gain as much weight to develop insulin resistance as do chubbier animals fed a high-fat diet alone. Moreover, those ill effects of branched chain amino acids, which include 3 of the 20 amino acids that are the building blocks of proteins, occurred only in the context of a high-fat diet.
"We've all made a big deal out of the fact that people in the U.S. eat too much fat and sugar, but we've underestimated the protein component," Newgard said. And indeed, he said, surveys have shown that most people who overeat don't show any particular prejudice toward one food group or another.
By comparing the metabolic profiles of obese versus lean people in the new study, the researchers found that key among the many differences between the two groups were elevated levels of BCAA in those who were overweight. They also showed that BCAA tend to climb along with insulin resistance, a condition that is a precursor to diabetes.
To further explore that correlation, they turned to studies of rats. Those controlled feeding studies revealed that, despite having reduced food intake and a low rate of weight gain equivalent to animals on standard chow, rats that consume more fat and BCAA were as insulin resistant as rats fed an HF diet. When added to a normal mouse diet, extra BCAA didn't result in insulin resistance.
I wonder if this is an artificial result. Does it apply to us eating real world diets? Would it happen with higher general protein diet and not just higher BCAA? Are there foods high in BCAA and low in the other amino acids?
Besides, rats' natural diet is nothing like humans', so I doubt that there is much relevance to comparing the effects of any particular diet between the two species. It would be like feeding a horse a meat diet than when the animal dies of starvation saying meat is bad for lions.
First, it's rats, so maybe limited application to humans. Second, this diet may well have not been low carbohydrate, which would increase tendency toward insulin resistance. The comments by the researcher don't sound convincing.
Animal chow is horrible stuff. I bet you could give humans an enormous host of problems if you fed them pelleted rat food.
If they wanted to establish that fat and protein together are bad, why did they feed the rats BCAA supplements instead of, you know, actual whole protein? I think it's telling that the rats fed fat *with* added BCAA actually ate less than those fed the unadulterated high-fat chow; I'd guess that adding a few pure amino acids rather than whole protein makes the chow taste crappy, even to a rat.
In any case, the likeliest villain here is the leucine, which stimulates insulin production quite substantially. While you get a decent chunk of leucine when you eat meat, I'd imagine that the process of digesting meat (or lentils, or soybeans, or various nuts... also good sources of leucine...) slows the intake enough that you don't jump-start your pancreas the way that you would by just ingesting leucine.
Anyway, all I conclude from this is that I don't want to be taking BCAA supplements.
According to Gary Taubes, it's only certain susceptible strains of rats that get fat on high-fat diets. And they have to be fed >30% fat (usually 40-60%) for it to happen (their normal diet is 2-6% fat). Other animals with digestive tracks closer to humans, such as pigs, cattle, and monkeys, all get fat on carbohydrate. Actually, so do many strains of rats on a high-sugar diet. There was a study in the 1970s where Anthony Sclafani let rats freely consume a selection of foods from the local supermarket. They got "super-obese." The rats preferentially fed on sweetened condensed milk, chocolate-chip cookies, and bananas, while not overeating cheese, pastrami, or peanut butter -- sugar over fat, apparently.
animals with digestive tracts closer to humans, such as pigs, cattle
Pigs I'll give you. But cattle? They have a four-stomach, multi-stage system that's not likely to be a good analog for any digestive tract other than another ruminant's.