Glucagon, Dietary Protein, and Low-Carbohydrate Diets

Glucagon is a hormone that plays an important role in blood glucose control. Like insulin, it's secreted by the pancreas, though it's secreted by a different cell population than insulin (alpha vs. beta cells). In some ways, glucagon opposes insulin. However, the role of glucagon in metabolism is frequently misunderstood in diet-health circles.

The liver normally stores glucose in the form of glycogen and releases it into the bloodstream as needed. It can also manufacture glucose from glycerol, lactate, and certain amino acids. Glucagon's main job is to keep blood glucose from dipping too low by making sure the liver releases enough glucose. There are a few situations where this is particularly important:

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Dogs Eating Carbs

Five years ago, I had an interesting conversation with a veterinarian friend about dog food. We were talking about diabetes in one of the dogs she was treating, and I remarked "that's what happens when you feed a carnivore carbohydrate". She gave me a funny look. At the time, I was seeing the world through the low-carb lens, and I remember thinking how bizarre it was that she didn't yield to my impeccable logic. As they say, live and learn.

The journal Nature published a fascinating paper on the evolution of the domestic dog today (1). Researchers compared the genome of wolves and domestic dogs to see what genetic changes accompanied domestication.

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The Potato Diet

In 2010, I wrote a series of blog posts on the health properties of potatoes (1, 2, 3). The evidence showed that potatoes are non-toxic, filling per calorie, remarkably nutritious, and can be eaten as almost the sole source of nutrition for extended periods of time (though I'm not recommending this). Traditional South American cultures such as the Quechua and Aymara have eaten potatoes as the major source of calories for generations without any apparent ill effects (3). This is particularly interesting since potatoes are one of the highest glycemic and most insulin-stimulating foods known.

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Nutrition Science Initiative (NuSI)

Some of you may have heard of an ambitious new nutrition research foundation called the Nutrition Science Initiative (NuSI). In this post, I'll explain what it is, why it matters, and how I feel about it-- from the perspective of an obesity researcher.

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Ancestral Health Symposium 2012

I recently returned from AHS12 and a little side trip to visit family. The conference was hosted at Harvard University through the Harvard Food Law Society. Many thanks to all the organizers who made it happen. By and large, it went smoothly.

The science as expected ranged from outstanding to mediocre, but I was really encouraged by the presence and enthusiastic participation of a number of quality researchers and clinicians. The basic concept of ancestral health is something almost anyone can get behind: many of our modern health problems are due to a mismatch between the modern environment and what our bodies "expect". The basic idea is really just common sense, but of course the devil is in the details when you start trying to figure out what exactly our bodies expect, and how best to give it to them. I think our perspective as a community is moving in the right direction.

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Interview with Aitor Calero of Directo al Paladar

Aitor Calero writes for the popular Spanish cooking and nutrition blog, Directo al Paladar ("straight to the palate"). We did a written interview a while back, and he agreed to let me post the English version on my blog. The Spanish version is here and here.

Without further ado, here it is:

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Why Did Energy Expenditure Differ Between Diets in the Recent Study by Dr. Ludwig's Group?

As discussed in the previous post, a recent study by Dr. David Ludwig's group suggested that during weight maintenance following fat loss, eating a very low carbohydrate (VLC) diet led to a higher metabolic rate (energy expenditure) than eating a low-fat (LF) diet, with a low glycemic index (LGI) diet falling in between the two (1). The VLC diet was 30 percent protein, while the other two were 20 percent. It's important to note that these were three dietary patterns that differed in many ways, and contrary to claims that are being made in the popular media, the study was not designed to isolate the specific influence of protein, carbohydrate or fat on energy expenditure in this context.

Not only did the VLC diet lead to a higher total energy expenditure than the LF and LGI diets, the most remarkable finding is that it led to a higher resting energy expenditure. Basically, people on the VLC diet woke up in the morning burning more energy than people on the LGI diet, and people on the LGI diet woke up burning more than people on the LF diet. The VLC dieters burned 326 more calories than the LF dieters, and 200 more than the LGI dieters.

It's always tempting to view each new study in isolation, without considering the numerous studies that came before it, but in this case it's essential to see this study through a skeptical lens that places it into the proper scientific context. Previous studies have suggested that:

1. The carbohydrate:fat ratio of the diet has little or no detectable impact on energy expenditure in people who are not trying to lose weight (2, 3).
2. The carbohydrate:fat ratio of the diet has little or no detectable impact on energy expenditure in people who are being experimentally overfed, and if anything carbohydrate increases energy expenditure more than fat (4, 5).
3. The carbohydrate:fat ratio of the diet has little or no detectable impact on energy expenditure during weight loss (6, 7, 8), and does not influence the rate of fat loss when calories are precisely controlled.

This new study does not erase or invalidate any of these previous findings. It fills a knowledge gap about the effect of diet composition on energy expenditure specifically in people who have lost weight and are trying to maintain the reduced weight.

With that, let's see what could have accounted for the differences observed in Dr. Ludwig's study.
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New Study: Is a Calorie a Calorie?

A new study in JAMA led by Dr. Cara B. Ebbeling and colleagues purports to challenge the idea that all calories are equally fattening (1). Let's have a look. When thinking about the role of calorie intake in body fatness, there are basically three camps:

1. Calories don’t matter at all, only diet composition matters.
2. Calories are the only thing that matters, and diet composition is irrelevant.
3. Calories matter, but diet composition may also play a role.

The first one is an odd position that is not very well populated. The second one has a lot of adherents in the research world, and there’s enough evidence to make a good case for it. It’s represented by the phrase ‘a calorie is a calorie’, i.e. all calories are equally fattening. #1 and #2 are both extreme positions, and as such they get a lot of attention. But the third group, although less vocal, may be closest to the truth.
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