Are low glycemic diets better for your heart?

How much we eat matters a whole lot, and the bottom line is that too many calories, no matter what their source, will lead to weight gain and the myriad of health consequences related to overweight, including increased risk of heart disease, diabetes, stroke and some cancers. 

But what we eat matters, too, and lots of study and experimentation addresses the issue of which foods and nutrients (fat varieties, protein, carbs) lead to better health and better chances of losing weight and keeping it off.  The connection between the fat in the diet -- more specifically the saturated fat component -- and heart health is a much-studied topic.  But could different carbs and protein matter just as much?

Low Glycemic eating pattern and heart disease risk

All carbohydrates are not created equal -- at least not by the way our body responds to them.

The glycemic index, developed initially for the treatment of diabetes, ranks carbohydrate-containing foods based on how they affect blood sugar levels when eaten in isolation. Carbs that break down quickly, like white bread and potatoes, have a high glycemic index, and those that release sugar into the blood stream more gradually, like fruit, have a low glycemic index. Foods are scored on a scale of 0 to 100.

Glycemic index’s proposed effect on both metabolism and health outcomes seems quite plausible: Blood glucose fluctuations elicit a cascade of hormonal reactions, which can potentially affect satiety, hunger, blood lipids and inflammation.

And indeed, a few short term studies show that a low glycemic diet can decrease hunger and control weight regain.  The glycemic index is taken into consideration in many popular weight management plans, including the South Beach Diet, Nutrisystem, the Zone diet and Sugar Busters.

And now, a new study in Circulation looks at how different weight maintenance diets -- differing in glycemic index and protein content -- affect heart disease risk.  The study group of about 500 overweight people first lost weight over 8 weeks on a low calorie diet.  After shedding about 8 percent of body weight the participants were randomly assigned to one of 5 diets, which they successfully maintained for 6 months:

• Low glycemic low protein
• High glycemic low protein
• Low glycemic high protein
• High glycemic high protein
• Control diet: healthy diet conforming to national standards

Heart disease develops over very long periods of time, so what the investigators studied were markers, known risk factors for heart disease, one of which was C-reactive protein (CRP), a protein found in the blood, and the levels of which indicate inflammation.  Low-level inflammation is believed to be the cause of many disease processes and to be prevalent in overweight people.

Here are the study’s main findings:

• During the 8 weeks of calorie restriction and rapid weight loss all the participants had a marked improvement in blood pressure, blood lipids (cholesterol profile) and CRP.
• During the 26 weeks of weight maintenance period only the two groups on a low glycemic diet experienced further reduction in CRP. Protein content and further weight loss didn’t affect the connection between low glycemic diets and lower CRP.
• Despite lower body weight, once the low-calorie diet was replaced by the maintenance diets, cholesterol and LDL (‘bad’ cholesterol) returned to baseline.
• And since I know you're wondering: The best diet for weight maintenance was the low glycemic/high protein one -- after 6 months the high glycemic/low protein group gained about 4.5 pounds more compared to the low glycemic/high protein group.

Could low glycemic diets affect inflammation?  The authors cite several studies that also found that low glycemic diets are associated with lower CRP, and suggest that high blood glucose after meals stimulates the expression of inflammatory genes.  

Is low glycemic the next Atkins?

I hope that after all these decades of going all-the-way with low carb, low fat and other simplistic, total sweeping rules – to no avail -- we’ve learned that nutrition is both exceedingly complex and at the same time practically quite simple.

Low glycemic eating patterns seem to have growing scientific support.  Low glycemic foods correspond quite often with the age-old understanding of what’s good to eat. Most highly processed grain products have a high glycemic index, whereas minimally processed grains, whole fruits, legumes, and non-starchy vegetables tend to have a moderate or low glycemic index.

On the other hand pure fructose and ice cream have a very low glycemic index, table sugar and high fructose corn syrup have only a moderate one, and potatoes and white rice are the root of all glycemic evil, with a glycemic index of about 100.

So clearly, glycemic index is only one of the parameters we need to think about when selecting carbs, but food choices cannot be made using glycemic index alone.

The glycemic index also has plenty of shortcoming: It’s difficult (and costly) to test the glycemic index of food, there’s inter-lab variability, the type and proportion of sugar or starch in a food affects glycemic index but so do a lot of other factors in the meal—the way the food’s been cooked, the presence of fiber, protein, fat, alcohol or acid all affect the glucose response—and there’s plenty of individual variability.  Finally, the glycemic index of the food matters much less than how much of that food you’re eating.   To really make the glycemic index useful you’ll need to calculate the glycemic load -- taking into account the glycemic index, the percentage of carbs in the food and the portion size – a better predictor of how your blood sugar will be affected by that certain meal component.

So while the glycemic index might be worth thinking about, especially for diabetics and overweight people, adhering to a healthy diet, rich in fruits, veggies and whole grains and avoiding highly processed junk is probably good enough practical advice for most of us –- and it has the added advantage of standing the test of time.

Dr. Ayala