December 22, 2014
No Silver Bullet…For Flawed Diet Studies
By Michael D. Shaw
Once reputed to be effective for killing werewolves, modern day silver bullets are seemingly magical solutions to complex problems. However, most of the time you see “silver bullet” in print it is in the negative as “XYZ is not a silver bullet against [fill in the blank].” And, in a double irony, according to tests run by ballistics experts, silver bullets aren’t even silver bullets. They tend to travel slower, with inferior target penetration, and are less accurate than conventional lead projectiles.
That’s why I had to smile at the recent headline from MedPageToday—“OmniCarb Study: Cutting Carbs No Silver Bullet.” This catchy headline refers to a study appearing in the December 17th issue of JAMA entitled “Effects of High vs Low Glycemic Index of Dietary Carbohydrate on Cardiovascular Disease Risk Factors and Insulin Sensitivity.”
The authors concluded that “In the context of an overall DASH-type diet, using glycemic index to select specific foods may not improve cardiovascular risk factors or insulin resistance.” On its face, this is a surprising finding. In an editorial that accompanies the study, Robert H. Eckel, M.D., of the University of Colorado Anschutz Medical Campus notes that…
“The unexpected findings of the study by Sacks et al. suggest that the concept of glycemic index is less important than previously thought, especially in the context of an overall healthy diet, as tested in this study. These findings should therefore direct attention back to the importance of maintaining an overall heart-healthy lifestyle, including diet pattern.”
Eckel’s comments are interesting. The Glycemic Index (GI) is determined by having healthy volunteers eat a particular food (and nothing else), while their blood glucose is being monitored for two hours. A low GI food will cause a smaller spike in blood glucose than a high GI food. As such, potato chips are superior to bananas, and dates are terrible compared to Snickers bars.
But wait. No one eats a single food and nothing else for two hours, right? And, if you mix foods, that completely throws off any glycemic index calculation. Put a pat of butter on that slice of white bread and the GI drops. Besides, many other factors can spike blood glucose, including “liver dump” (glycogen release by the liver), and hormones such as cortisol.
So, Dr. Eckel, whom–besides those who profit from GI–think it is “important”? And, what about that “overall healthy diet”?
That would be the DASH-type diet, which formed the basis of the study, to which carbs and GI values were the variables. Simply put, the DASH (Dietary Approaches to Stop Hypertension) diet is a warmed-over Mediterranean diet, with somewhat more carbs and a drastically lowered sodium content. National Heart, Lung, and Blood Institute geeks would freak at the real Mediterranean diet and its typical sodium level of 4200 milligrams per day.
DASH fanboys continue to tout its anti-hypertensive properties, but the facts on how much reduction actually occurs are not so impressive:
- 2.42 mm Hg systolic and 1.00 mm Hg diastolic, in those with normal blood pressure
- 5.39 mm Hg systolic and 2.82 mm Hg for diastolic, in hypertensives
There’s also the matter of what Sacks et al. consider high and low carb diets. In their fantasy world, low is 40% carbs and high is 58% carbs. Renowned nutritionist, fellow HND columnist, and author of popular dietary counter books Jo-Ann Heslin states that 30% would be the maximum for a diet to be considered “low carb.” Indeed, low carb aficionados would tend to run in the 20s or even lower.
Likewise, nutritionist Diane Kress, friend of this column–known for her Metabolism and Diabetes Miracle books–reminds us that there is more to improving health via dietary adjustment than simplistic manipulations of GI and carb content. She adds that the study in question seems to be designed to make low carb look ineffective.
In fairness, by using controlled feeding, whereby all meals are supplied to the participants, the authors do have a pretty good handle on what is being consumed. Compare this to the hundreds of studies based on participant self-reporting. In a brief interview, Sacks insisted that there is no official definition of low and high carb, which might technically be correct–even if most authorities would disagree with his.
Thus, we have a study that overplays the value of glycemic index, misstates what low and high carb diets are, and is built around the overrated DASH diet. With no silver bullet in sight.