Gabor Erdosi gave a great talk recently.
One of the slides really ties things together for me. There’s a debate in the keto community over which macronutrient provides the most satiety. We all agree it is not carbohydrates. Some of us say it’s fat which most satisfies our hunger. Others say it’s protein. I tend towards the protein side of the question but have found it to still be an open issue.
Role of Hormones – Ghrelin and Leptin
The hunger hormone Ghrelin is the key to refeeding. Roughly speaking, if your Ghrelin goes below a baseline you are less hungry. If it goes above the baseline you are more hungry.
Ghrelin, as compared to leptin, controls short term hunger. From this paper (Klok MD1, Jakobsdottir S, Drent ML. The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review. Obes Rev. 2007 Jan;8(1):21-34.:
Leptin is a mediator of long-term regulation of energy balance, suppressing food intake and thereby inducing weight loss. Ghrelin on the other hand is a fast-acting hormone, seemingly playing a role in meal initiation.
Gabor cited a study which compared human’s Ghrelin response to the three macronutrients (Karen E. Foster-Schubert, Joost Overduin, Catherine E. Prudom, Jianhua Liu, Holly S. Callahan, Bruce D. Gaylinn, Michael O. Thorner, David E. Cummings; Acyl and Total Ghrelin Are Suppressed Strongly by Ingested Proteins, Weakly by Lipids, and Biphasically by Carbohydrates, The Journal of Clinical Endocrinology & Metabolism, Volume 93, Issue 5, 1 May 2008, Pages 1971–1979).
Here is the key graph from the study.
Let’s look at each of the three macronutrients and their effect on hunger via their impact on Ghrelin levels.
Carbohydrates provided the greatest drop in Ghrelin for the first 140 minutes. They also have a significantly bigger Area Under the Curve (AUC) during that period. After that the slope rises dramatically. By 240 minutes the graph shows Ghrelin crossing over the baseline and going above the baseline. The slope up is shown roughly in the red line below.
That’s why you feel hunger when you eat carbohydrates and why you want to eat again just a couple of hours later. For me this comes to mind:
It’s the slope of the line up that drives you to want to refeed.
They keto community is correct. Fat (lipid) does drop Ghrelin. It does a decent job since it stays below baseline for many hours. Here’s the rough area under the curve (AUC) for Ghrelin after eating fat during those hours.
This explains to me why some people feel that Bulletproof Coffee works for them. It helps them not be hungry for hours. Fat alone help you stay below baseline levels of Ghrelin.
Here’s where the paper answers the question asked in the opening paragraphs of this page. Which macronutrient provides the best depression of Ghrelin? Clearly protein wins the battle. Here’s the AUC for protein:
Protein vs Fat
Putting both Protein and Fat AUCs together something interesting becomes clear.
There’s nothing that fat does that protein doesn’t do even better for depressing Ghrelin levels. Particularly at several hours in. They both keep the Ghrelin levels below baseline but protein does it longer and deeper. Yes, you do get hungry again when you return to near baseline at 6 hours in.
The debate will continue in the keto community until people actually examine the science. It seems pretty clear that protein is a superior choice to fat when taken in isolation. Both together seem like a fine choice so on some level both sides are correct.
Bulletproof Coffee or Bacon and Eggs? Bacon and eggs for me, thanks.