Thursday, September 18, 2014

My AHS14 Talk on Leptin Resistance is Posted

The Ancestral Health Society just posted a video of my recent talk "What Causes Leptin Resistance?"  Follow the link below to access it.  Enjoy!

What Causes Leptin Resistance?


Monday, September 8, 2014

Thoughts on the McDougall Advanced Study Weekend

For those of you who aren't familiar with him, Dr. John McDougall is a doctor and diet/health advocate who recommends a very low fat, high starch, whole food vegan diet to control weight and avoid chronic disease.  He's been at it for a long time, and he's a major figure in the "plant-based diet" community (i.e., a diet including little or no animal foods).

Dr. McDougall invited me to participate in his 3-day Advanced Study Weekend retreat in Santa Rosa, CA.  My job was to give my talk on insulin and obesity, and participate in a panel discussion/debate with Dr. McDougall in which we sorted through issues related to low-carb, Paleo, and the health implications of eating animal foods.  I was glad to receive the invitation, because I don't see myself as a diet partisan, and I believe that my evidence-based information is applicable to a variety of diet styles.  I saw the Weekend as an opportunity to extend my thoughts to a new community, challenge myself, and maybe even learn a thing or two.  It was particularly interesting to compare and contrast the Advanced Study Weekend with the Ancestral Health Symposium, which is more Paleo- and low-carb-friendly.

General Observations

The attendees were a lot older than AHS attendees.  I estimate that most of them were in their 60s, although there were some young people in attendance.

I don't place too much emphasis on peoples' personal appearance at conferences like this.  You don't know what a person's background, genetics, or personal struggles may be, you don't know how closely they adhere to the program, and you don't know to what degree a group of people might be self-selected for particular traits*.  But I will note that Dr. McDougall, his family, and many of the other starch-based/plant-based diet advocates tended to be extremely lean with low fat and muscle mass.  They also tended to have a healthy and energetic appearance and demeanor.  As I would expect, decades of exceptionally high starch intake hasn't made them obese or obviously ill.

Thursday, September 4, 2014

What about the Other Weight Loss Diet Study??

The same day the low-fat vs low-carb study by Bazzano and colleagues was published, the Journal of the American Medical Association published a meta-analysis that compared the effectiveness of "named diet programs".  Many people have interpreted this study as demonstrating that low-carbohydrate and low-fat diets are both effective for weight loss, and that we simply need to pick a diet and stick with it, but that's not really what the study showed.  Let's take a closer look.

Johnston and colleagues sifted through PubMed for studies that evaluated "named diet programs", such as Ornish, Atkins, LEARN, Weight Watchers, etc (1).  In addition, the methods state that they included any study as low-carbohydrate that recommended less than 40% of calories from carbohydrate, was funded by the Atkins foundation, or was "Atkins-like".  These criteria weren't extended to the low-fat diet: only studies of name-brand low-fat diets like the Ornish diet were included, while the meta-analysis excluded low-fat diet studies whose guidelines were based on recommendations from government and academic sources, even though the latter group represents the majority of the evidence we have for low-fat diets.  The inclusion criteria were therefore extremely asymmetrical in how they represented low-carb and low-fat diets.  This fact explains the unusual findings of the paper.

The abstract immediately activated my skeptic alarm, because it states that at the one-year mark, low-carbohydrate diets and low-fat diets both led to a sustained weight loss of about 16 pounds (7.3 kg).  Based on my understanding of the weight loss literature, that number seems far too high for the low-fat diet, and also too high for the low-carbohydrate diet.

Monday, September 1, 2014

Low-carbohydrate vs. Low-fat diets for Weight Loss: New Evidence

A new high-profile study compared the weight loss and cardiovascular effects of a low-carbohydrate diet vs. a low-fat diet.  Although many studies have done this before, this one is novel enough to add to our current understanding of diet and health.  Unlike most other studies of this nature, diet adherence was fairly good, and carbohydrate restriction produced greater weight loss and cardiovascular risk factor improvements than fat restriction at the one-year mark.  Yet like previous studies, neither diet produced very impressive results.

The Study

Lydia A. Bazzano and colleagues at Tulane University randomly assigned 148 obese men and women without cardiovascular disease into two groups (1):
  1. Received instructions to eat less than 40 grams of carbohydrate per day, plus one low-carbohydrate meal replacement per day.  No specific advice to alter calorie intake.  Met regularly with dietitians to explain the dietary changes and maintain motivation.
  2. Received instructions to eat less than 30 percent of calories from fat, less than 7 percent of calories as saturated fat, and 55 percent of calories from carbohydrate, plus one low-fat meal replacement per day.  No specific advice to alter calorie intake.  This is based on NCEP guidelines, which are actually designed for cardiovascular risk reduction and not weight loss.  Met regularly with dietitians to explain the dietary changes and maintain motivation.
Participants were followed up for one year, with data reported for 3 month, 6 month, and 12 month timepoints.  This study actually measured body fat percentage, but unfortunately did so using bioelectrical impedance (like on some bathroom scales), which is essentially meaningless in this context.

Results

Monday, August 18, 2014

Science of Nutrition Podcast

I recently did an interview with Seth Yoder, who has a master's degree in nutrition science and writes the blog The Science of Nutrition.  Seth caught my attention recently with his withering review of The Big Fat Surprise, the latest book to claim that ideological/incompetent scientists and public policy makers got the science of nutrition backward and we should all be eating low-carb, high-fat, high-meat diets.  I was impressed by how deeply Seth dug into the reference list, and how well he picked up on subtle but troubling misrepresentations of the evidence.

Last week, Seth and I got together at a local brewpub to do an interview.  We were joined by Carrie Dennett, an MPH/RDN who has a nutrition blog and writes for the Seattle Times.  I'd probably do a lot more interviews if I could ride my bike to them and have my interviewer buy me a drink.

Speaking of drinks, by the end of the interview I had a little buzz-- you might hear it in my voice if you listen closely.  As usual, I had plenty to say about body fat regulation, food reward, and other topics, with plenty of side trips to discuss particularly fascinating studies.  Also, the word of the day was 'compelling'.

Enjoy the interview!

Tuesday, August 5, 2014

Can Hypothalamic Inflammation and Leptin Resistance be Reversed?

A new study by yours truly begins to address the key question: can hypothalamic inflammation and leptin resistance be reversed?

Leptin is the primary hormonal regulator of body fatness in the human body (1).  Secreted by fat tissue, it acts in many places in the body, but its most important effects on body weight occur via the brain, and particularly a brain region called the hypothalamus.  The hypothalamus is responsible for keeping certain physiological variables within the optimal range, including blood pressure, body temperature, and body fatness.

In obesity, the brain loses its sensitivity to leptin, and this causes the body to begin 'defending' a higher level of body fatness, analogous to how a person with a fever 'defends' a higher body temperature (1).  Once a person has become obese, it's difficult to return to true leanness because this system vigorously opposes major fat loss.  Leptin resistance makes fat loss more difficult.

In rodent models, leptin resistance is caused at least in part by inflammatory signaling in the hypothalamus.  We can observe this in multiple ways, but one common way is to look at the appearance of specific cells in the brain that change number, size, and shape when inflammation is present (2).  These cells are called microglia and astrocytes.  In addition to the work in rodents, we've published preliminary evidence that these same inflammatory changes occur in the hypothalamus of obese humans (2).

A key question is whether or not these inflammatory changes can be reversed.  Is a person with leptin resistance doomed to have it forever, undermining fat loss efforts for the rest of his or her life?  Or can it be corrected, possibly allowing easier and more sustainable fat loss?  We just published a study in Endocrinology that begins to answer this question, using a mouse model of dietary obesity (3).  I'm co-first author of this study along with my colleague Kathryn Berkseth, MD.  My former mentor Mike Schwartz, MD is senior author.

The Study