Do carbs “spike” leptin?
This seems to be a central tenet to Dr. Rosedale’s science, but it appears to be false according to Carbsane.
Is there any more evidence either way that anybody wants to share?
Yes, carbs raise leptin, but not in a "spiky" fashion.
Edited to answer Evelyn:
I think it is important to differentiate postprandial effects from chronic effects, ie. which show alteration of its pulsatile/circadian secretion. For instance:
(...) the high GI CHO diets, A and C, altered the 24-hr leptin profiles. Serum leptin rose >above the 0800 hr baseline as early as 1300 hr, whereas leptin concentrations with diets B and D did not rise above baseline until 2400 hr. The leptin AUCs from 1230 hr to 2400 hr for diets A and C were significantly higher than for diets B and D (P < 0.0001) using the first model.
The 24-hr AUCs for leptin on diets A and C were significantly greater than the AUCs for leptin on diet B (P < 0.003) using the second model. Meals indicated as solid arrows, open arrows equal snacks.
You can see that approximately at the 3 hour mark, leptin concentrations start to rise in both normal and obese women. So there seems to be an steady increase, not a spike, but an increase in the end, which was correlated to carbohydrate but not fat (note the concentration of leptin in obese and lean in the picture above):
In the study you cite (A High Glycemic Meal Suppresses the Postprandial Leptin Response in Normal Healthy Adults), they measured the leptin response 120min after, and as we have seen, the increases seem to start 2-3 hours later.
I havent researched much, but from what I remember, glucose stimulates leptin expression. The immediate postprandial rise in insulin and BG following a carbohydrate rich meal, would stimulate secretion of leptin, which would show higher levels more delayed than the insulin/glucose response or a different pattern of peaking, like seen in the first study cited.
For those who don't follow my blog, you might be interested in this post: http://carbsanity.blogspot.com/2011/10/24-hour-leptin-profiles-sleep-off-your.html
There is a sampling of 24 hour leptin level profiles there.
Does what you eat (and when you eat it) influence leptin levels? Seems so. But not in what is traditionally understood to be a postprandial spike. Indeed what is influenced is the diurnal (turns out middle of the night) rise in leptin.
I posted these in the comments on her blog yesterday
This pronounced fall in serum leptin in asso- ciation with reduced carbohydrate intake before sub- stantial loss of body fat suggests a role for leptin in defending the body’s carbohydrate stores and impli- cates leptin in the satiating effects of carbohydrate.
In conclusion, the results of the present study demonstrated that a carbohydrate meal induces a greater postprandial leptin response than an isoenergetic fat meal and that this response is correlated to the physiological postprandial insulin response.
Her reply was that
Your second study is actually the one I blogged on previously from which the first graphic in this post came. I wouldn't call the delayed rise in leptin levels a "spike" by any stretch of the imagination. The other study discusses leptin levels going down with carb restriction. Given that this occurs in fasting, and many features of fasting/starvation are thought to be linked to glycogen depletion/glucose availability, this is no surprise.
I tend to agree with her in spite of the authors' findings. I am going to keep looking into this....
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