I was a bit surprised by the conclusions reached in the recent issue of the Archives of Internal Medicine - Comparison of 4 Diets of Varying Glycemic Load on Weight Loss and Cardiovascular Risk Reduction in Overweight and Obese Young Adults - in which researchers concluded that "Both high-protein and low-GI regimens increase body fat loss, but cardiovascular risk reduction is optimized by a high-carbohydrate, low-GI diet."
So, as you may have guessed - I was off to reading the full-text and data to understand how the conclusion was reached.
As suspected, total cholesterol and LDL were the ever "all important" markers used to determine cardiovascular risk reduction.
Each time I come upon another study that fails to include other potent measures of cardiovascular risk as part of the conclusions, I'm less surprised. Some days it seems the diet-heart-lipid hypothesis is so entrenched in the conventional wisdom we're doomed to just keep on keeping on with it, stumbling along while ignoring other critical markers in our "vein" [pun intended] attempt to convince the population to eat less fat while continuing to eat a diet rich with carbohydrate!
Who are they kidding?
For one thing, the study was just twelve weeks - as we hear so often from the low-carbohydrate diet critics, such a short period is way too little time to make such a sweeping conclusion that reduction of cardiovascular risk is "optimized" by a diet. And you know what, twelve weeks is too little time! I've never had an issue with that criticism leveled at studies of short duration for low-carbohydrate diets. I do take issue with dietary studies of similar short duration touted as examples to "optimize" reduction of cardiovascular risk!
Add to that the researchers make no mention of the insignificant reduction to blood glucose, the miniscule increase in HDL, the almost non-existent reduction in triglycerides nor the inconsequential down tick in glucose levels. These other risk markers had no spectacular improvements, yet the researchers concluded the high carbohydrate-low GI diet offered "optimized" cardiovascular risk reduction.
Reducing the risk of cardiovascular disease is a lot more than just getting total cholesterol and LDL heading south - I believe they also need to happen in conjunction with other overall improvements - significant reduction in triglycerides, improved glycemic control, improved insulin and improvements in TC:HDL and HDL:TG. At the end of the day, LDL may not be the end-all be all marker we make it when we look at the bigger picture with what may be more important risk markers.
While the old guard still holds sway and appears to influence researcher conclusions to focus on LDL and total cholesterol, there is compelling evidence (as I've pointed out previously) that we must be investigating other markers if we're going to truly make a difference in the lives of millions with or at risk for cardiovascular disease.
When we look at the total list of risk markers we find the high carbohydrate-low GI diet was not necessarily the "optimal" diet for long-term cardiovascular health. In fact, none of the diets were all that spectacular with overall improvements to stand out. In this particular study, the results at twelve weeks were so mixed they're really clinically insignificant in my view, especially if the intent of such studies is to increase our knowledge and significantly impact all markers in those at risk.
If we aspire to take a broader view of risk reduction and seek to really improve overall health, a good example is found in the study published last year by Yancy et al. I highlight this study because of the similar duration and calorie intake with focus on low carbohydrate, which is naturally low for glycemic index and glycemic load, but dramatically different macronutrient mix for consumption of carbohydrate, protein and fat. It is probably the best to use here in an attempt for an apples-to-apples comparison.
Yancy et al included just 38.9g average carbohydrate, 93.5g average total fat and 98.5g protein in 1418 calories; McMillian-Price et al (above) included 200g carbohydrate, 36g total fat and 63g protein in 1438 calories. Yancy et al does not detail consumption of saturated fat, but it's a fair assumption it was significantly higher for dieters in his study given the total fat intake along with the higher protein intake.
If dietary fat is truly detrimental - especially saturated fat - we should see some major increased risks in those following the diet in Yancy, right?
Funny thing - we find significantly greater improvements in those subjects following the diet in Yancy than we do in McMillan. With one glaring exception - LDL cholesterol. Let's take a look:
Yancy 131.4kg reduced to 122.7kg (-8.7kg)
McMillian-Price 87.1kg reduced to 82.3kg (-4.8kg)
(to be fair, Yancy et al was an additional four weeks in duration)
Yancy 4.61 reduced to 4.54 (-0.70)
McMillian-Price 4.71 reduced to 4.53 (-0.18)
Yancy .92 increased to .99 (+0.07)
McMillian-Price 1.16 increased to 1.21 (+0.05)
Yancy 2.51 increased to 2.77 (+0.26)
McMillian-Price 2.9 reduced to 2.73 (-0.17)
Yancy 2.69 reduced to 1.57 (-1.12)
McMillian-Price 1.39 reduced to 1.34 (-0.05)
Yancy 5 reduced to 4.5 (-0.50)
McMillian-Price 4.16 reduced to 3.95 (-0.21)
Yancy 2.92 reduced to 1.58 (-1.34)
McMillian-Price 1.19 reduced to 1.10 (-0.09)
Yancy 9.8 reduced to 7.57 (-2.23)
McMillian-Price 4.95 reduced to 4.88 (-0.06)
The question begs - why are we still bent on LDL cholesterol as an end-all-be-all marker of improvement or reduction of risk? It's clear from the data above that subjects experienced greater overall improvements following the low-carbohydrate diet than they did following the high carbohydrate-low GI diet that was also low in fat and protein.
It's pretty easy to do the math - McMillian et al provided 22% of calories a fat (36g in 1417 calories) and Yancy et al provided 59.3% of calories as fat (93.5g in 1418 calories).
The subjects in Yancy et al consumed not only relatively more fat (percentage of calories), but absolutely more fat (grams consumed daily) - they ate 3-times the fat as those in McMillian et al. In fact, those in the Yancy et al study consumed more fat than the average American does each day if the American Heart Association numbers are correct at 81.4g total fat per day per person!
They ate more fat and still had greater improvements in the broader list of risk markers, except their LDL increased slightly.
But, after decades of being told it's the dietary fat we must reduce (with no convincing data), we're now seeing a transition in the message to eat a diet that is low in fat and low GI, but still rich with carbohydrate. Aside from both diets offering the ability to lose weight, the data above clearly shows that after twelve weeks, other than LDL cholesterol levels, no other significant improvements were found in subjects following the high-carbohydrate/low-GI/low-fat diet.
While it is politically correct to reach such a conclusion, it's again a great example of how dogma can over-ride hard data. Shouldn't a conclusion of "optimized" reduction of cardiovascular risk also include HDL? Triglycerides? Glucose? Insulin? TC:HDL ratio? TG:HDL ratio?
The hard data here is that none of the four dietary interventions McMillian et al investigated did much of anything in twelve weeks other than allow for some weight loss and two of the four resulted in a reduction in LDL.
Simply put - that's not enough time nor improvement to make a sweeping and strong conclusion that a high carbohydrate, low-GI diet (the one that reduced LDL the most) optimizes cardiovascular risk reduction!