A new study just published in the AMA Journal compared three diets: a low-fat diet, a low-glycemic/Mediterranean diet, and a low-carb/Atkins-like diet.
Although participants burned the most energy on the low-carb diet, researchers found that it came at a cost of "increases in cortisol, a stress hormone, and a measure of inflammation called CRP, which can raise the risk of developing heart disease and diabetes."
Those who are versed in reading scientific journals, can you comment on this? Why would low-carb increase inflammation? Does it have anything to do with the quality of food the participants were eating?
If it's improperly done I can see where inflammation may be increased. The metabolism of meats (especially red grain-fed meats, as well as the cooking style: barbecue (char grilling being one destroyer of meat's nutritional value) generates a lot of free radicals and I can see where that could potentially raise levels of inflammation. This study is not specific on the type of low-carb diet followed on the low-carb/Atkin's style diet but I will wager that there were likely participants who were not as careful as they should be about where exactly their proteins came from, as well as how they balanced it with healthy low glycemic root starches (say, sweet potato vs. potato), quinoa, etc... and plenty of vegetables with a smattering of fruit.
The balance of anti-inflammatory and pro-inflammatory fats and oils is altered by animal diet- just like our own bodies are altered when our diets are full of too much corn and sugar. This is a scientifically investigated fact. Can't refer to journals as I have graduated college and don't have access to the databases, but Loren Cordain's speaking and writing on the Paleo Diet is informative. I'd look up whatever resources he cites.
The preface really speaks about food quality, like you said, IMO.
A low-carb, Atkins Diet, in a casual sense, can really improve metabolism, blood sugar regulation and various health markers. That doesn't mean it paid attention at all to other things.
A traditional Atkins low-carb approach puts very little emphasis on quality and advocates a lot of controversial things like artificial sweeteners and refined carbohydrate substitutes like like coconut flour, almond flour, etc. Highly-processed foods are also fine as long as their net carbs are low.
You can eat a Ketogenic diet but if you're doing so by eating a ton of low quality/processed meat, food additives, articial sweeteners and a lot of fake stuff, you might be just as bad off in the long run as eating a SAD outside of being less insulin-resistant and maybe a lower weight.
The article (freely available) is here: http://jama.jamanetwork.com/article.aspx?articleid=1199154
1) The study is too small to draw meaningful conclusions. 21 participants is a ridiculously low number. That said, it was a crossover study (all participants tried all three diets), so that makes it more interesting.
2) The low-carb diet was VLC, 10% calories from carbohydrates. The authors even comment, "Main study limitations are the relatively short duration of the test diets and the difficulty extrapolating findings from a feeding study to a more natural setting, in which individuals consume self-selected diets. In particular, the very low-carbohydrate diet involved more severe carbohydrate restriction than would be feasible for many individuals over the long term. Therefore, the study may overestimate the magnitude of effects that could be obtained by carbohydrate restriction in the context of a behavioral intervention."
3) There is no mention of food quality with regards to the VLC diet. On the other hand, "The low–glycemic index diet aimed to achieve a moderate glycemic load by replacing some grain products and starchy vegetables with sources of healthful fat and low–glycemic index vegetables, legumes, and fruits"
That a low-carb diet increases cortisol should be obvious. Cortisol is one of the main long term blood glucose regulators, and if insufficient amounts of carbohydrates are consumed, gluconeogenesis will be up-regulated through increased cortisol production.
As for the increased inflammation, the low carb diet STILL decreased CRP levels dramatically from baseline, just slightly less so than the low-GI and low-fat diets. The levels of plasminogen activator inhibitor 1 were however lower in the VLC diet, so I don't know whether you can really say inflammation was higher in the VLC condition.
As others have said as well, we don't have information on the types and quality of food consumed, so that could be a big confounding variable.
I 100% agree that when I was in my "low-carb" phase, the quality of my food was terrible. High consumption of O6 PUFAs, crap processed meat (not always, but a fair amount). However, I did actually have a significant improvement in my health, including autoimmune/inflammatory conditions. I attribute that to reduced consumption of gluten and grains. My cortisol was so high normally, that any reduction would have been an improvement.
So on that line, I wonder if they compared the coritsol to baseline levels or if it was compared to the people on the other diets. Obese people would generally have higher cortisol levels to begin with.
Fortunately, I have learned that the quality of my food really does matter and now moderately low carb plus paleo eating has made me even better.
With Ludwig, the lead guy on the study, I have to wonder if he stacked the deck in low-glycemic diet's favor. If even on an unconscious level. He has long been known as a low glycemic kida guy (as opposed to blatent LC) so I'm not suprised to see his study - or at least his interpertaion it- lend more overall support for a low GI diet than a brute LC diet. In much the same way I'm never surprised to see a study by a vegan lend more support for a vegan diet.
That's why I love the A to Z study. The low-carb diet did best, and the lead author was a vegetarian, but intellectually honest enough to admit the LC diet did better than the Ornish diet. In fact, he says the Ornish diet tended to raise the triglyceride levels of the study participants. Which of course is no big surprise to most of us.
Compared to the other diets, the low carb diet produced the smallest decrease in (resting and total) energy expenditure, a greater decrease in leptin (perhaps indicating a greater decrease in leptin resistance), better insulin sensitivity, lower triglycerides, and lower PAI-1 levels. These are all points in favor of the low carb diet in my mind.
Compared to other diets, CRP levels were higher in the LC group. However, all diets produced a decrease in CRP levels compared to baseline (which was 1.75) and ultimately the difference between the 3 diets was hardly significant (.78, .76, and .87). I'm critical of the author statement that low carb diets may increase CRP; this depends on context. According to the American Heart Association a CRP below 1 is considered "low risk". The low carb diet produced a CRP of .87.
The cortisol reading was interesting because it actually did increase in the LC group both compared to baseline and the other diets. I suspect cortisol increased to support gluconeogenesis; this effect was likely accentuated due to the high protein intake (30% of calories).
And as some have stated, diet quality may have had an effect. I suspect low intakes magnesium, vitamin C, and other nutrients more likely to be lacking in the LC group could have produced such effects on cortisol (and CRP).