March 02, 2008
Low Fat Diets Better For Heart Than Low Carbo Diets?

I'm far from convinced. But here's yet another round in the ideal diet debate.

Low-fat diets are more effective in preserving and promoting a healthy cardiovascular system than low-carbohydrate, Atkins’-like diets, according to a new study by researchers at the Medical College of Wisconsin in Milwaukee.

The study, published in the February edition of the scientific journal Hypertension, was led by David D. Gutterman, M.D., Northwestern Mutual Professor of Cardiology, professor of medicine and physiology, and senior associate dean of research at the Medical College. Shane Phillips, M.D., a former Cardiology faculty member at the Medical College, and now assistant professor in the department of physical therapy at the University of Illinois - Chicago, was the lead author.

Mind you, this is not the first study to address the question of fats versus carbohydrates for heart health and it likely won't be the last. The issue is not settled.

These scientists are quite sure that higher fat content does you more harm than higher carbohydrate content. My reaction: it depends.

“Low-carbohydrate diets are significantly higher in total grams of fat, protein, dietary cholesterol and saturated fats than are low-fat diets. While a low-carbohydrate diet may result in weight loss and improvement in blood pressure, similar to a low-fat diet, the higher fat content is ultimately more detrimental to heart health than is the low-fat diet suggested by the American Heart Association,” points out Dr. Phillips.

“The higher fat content of a low-carbohydrate diet may put dieters at an increased risk of atherosclerosis (hardening of the arteries) because low-carbohydrate diets often reduce protection of the endothelium, the thin layer of cells that line the blood vessels of the circulatory system. The reduced production from the endothelium of nitric oxide, a specific chemical, puts the vessel at higher risk of abnormal thickening, greater clotting potential, and cholesterol deposition, all part of the atherosclerosis process,” says Dr. Gutterman.

What does the carbs versus fats debate depend on? Which fats. Which carbohydrates. Also, what particular genes do you have?

Take carbohydrates for example. They do not all break down into simple sugars in the intestines at the same speed. The ones that break down slowly (they have low glycemic index) enter the blood stream more slowly than the ones that break down quickly (they have high glycemic index). A rapid rise in blood sugar has harmful effects. Plus, the simple sugars fructose and glucose do not get metabolized the same way. Glucose transport gets regulated with insulin for example. So not all carbohydrates are equal.

What I really want to see: A comparison where one group eats unrefined very low glycemic index carbs while another group eats refined high glycemic index carbs. Then 3 other groups should eat polyunsaturated, monounsaturated, and saturated fats. But even that split isn't fine enough. Still, such a comparison would be a good start.

These researchers see fats as worse for the cardiovascular system because the low carb diet participants showed less artery dilation than the low fat diet participants.

Over a six-week period, the researchers found reduced flow-mediated dilation in the arm artery in participants who were on the low-carbohydrate diet. Reduced flow-mediated dilation, as measured in this study, is an early indicator of cardiovascular disease. On the other hand, flow-mediated dilation improved significantly in participants on the low-fat diet suggesting a healthier artery which is less prone to developing atherosclerosis.

“We observed a reduction in brachial artery flow-mediated dilation after six weeks of weight loss on a low-carbohydrate, Atkins’-style diet,” Dr. Gutterman says.

A diet high in nuts would be high in fats. But it would be higher in less saturated fats and higher in arginine that promotes nitric acid production and capillary dilation. So I don't think the question of ideal diets is as easy as these researchers make it sound.

For the sake of argument, imagine that those who ate the low carb diet kept their weight down for longer periods of time. That benefit might outweigh other costs and benefits. We need to know more about the longer term effects of these diets. Does the low carbo diet do a better job of keeping off weight?

The researchers point out that the low carbo diet had less folic acid. But that's easily remediable by taking a pill or by eating green leafy vegetables (which are high in fiber too and have other good stuff in them).

Low-carbohydrate diets were also found to have significantly less daily folic acid than low-fat diets. Folic acid is thought to be helpful in reducing the likeliness of heart disease. This protective effect results from the antioxidant property of folic acid and its ability to lower levels of homocysteine, a naturally occurring amino acid that can be dangerous at elevated levels.

Low glycemic index beans also are good sources of folic acid. Check out this glycemic index database and try to shift your diet toward lower glycemic index foods. Those foods tend to be healthier for other reasons as well.

Share |      Randall Parker, 2008 March 02 08:00 PM  Aging Diet Heart Studies

Jim Rose said at March 3, 2008 5:55 AM:


I agree with almost everything in Randall's analysis. I feel the article being discussed is more of an opinion piece than serious research. However, it and similar serious research lead to an interesting observation. Namely,

The combination of fat and carbohydrates seems to lead to significantly worse outcomes than when either fat or carbohydrate is dominant in the diet . Why is this?

Two responses spring to mind. (1) these confections directly lead to overweight since the carbohydrate (read sugar) stimulates the appetite while the fat packs on the calories. (2) More interestingly, there may be a conflict in the cellular processing of these types of food. Fat and carbohydrate are metabolized using different biochemical pathways. I have seen it argued that these pathways conflict. Thus a person that eats mainly carbohydrates would be using a single fairly efficient metabolic pathway. Similarly, a person eating mainly fat would use a different but also fairly efficient pathways. However, it is argued that the combination of fat and carbohydrate tries to invoke both metabolic pathways simultaneously and thus bolixes up the works. The cell doesn't know what to do with the fat, which is disposed of inappropriately

JohnN said at March 4, 2008 11:00 PM:

Carb and fat are metabolized on the same biochemical pathway, just opposite directions.
The body requires insulin to move glucose (broken down from carb) into cells while fat is insulin-neutral. Worse yet with the present of insulin fat is moved into adipose tissue for storage. Now consider an opposite situation: if you manage to keep carb intake and hence insulin production low, the body can metabolize the fat intake and move fat out of the adipose tissues for consumption as well.
One just has to read the report to see how the conclusion of that study is reached. I don't think there's enough emphasis on the health benefits of keeping insulin level low.

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