Why Do We Eat? A Neurobiological Perspective. Part III

In the first post, I explained that all voluntary actions are driven by a central action selection system in the mesolimbic area (the reward system).  This is the part of you that makes the decision to act, or not to act.  This system determines your overall motivation to obtain food, based on a variety of internal and external factors, for example hunger, the effort required to obtain food, and the sensory qualities of food/drink.  These factors are recognized and processed by a number of specialized 'modules' in the brain, and forwarded to the reward system where the decision to eat, or not to eat, is made.  Researchers divide food intake into two categories: 1) eating from a true energy need by the body (homeostatic eating), e.g. hunger, and 2) eating for other reasons (non-homeostatic eating), e.g. eating for social reasons or because the food tastes really good.

In the second post of the series, we explored how the brain regulates food intake on a meal-to meal basis based on feedback from the digestive system, and how food properties can influence this process.  The integrated gut-brain system that accomplishes this can be called the satiety system.

In this post, we'll explore the energy homeostasis system, which regulates energy balance (energy in vs. energy out) and body fatness on a long term basis.

The Energy Homeostasis System

Why Do We Eat? A Neurobiological Perspective. Part II

In the last post, I explained that eating behavior is determined by a variety of factors, including hunger and a number of others that I'll gradually explore as we make our way through the series.  These factors are recognized by specialized brain 'modules' and forwarded to a central action selection system in the mesolimbic area (the reward system), which determines if they are collectively sufficient cause for action.  If so, they're forwarded to brain systems that directly drive the physical movements involved in seeking and consuming food (motor systems).

The term 'homeostasis' is important in biology.  Homeostasis is a process that attempts to keep a particular factor within a certain stable range.  The thermostat in your house is an example of a homeostatic system.  It reacts to upward or downward changes in a manner that keeps temperature in a comfortable range.  The human body also contains a thermostat that keeps internal temperature close to 98.6 F.  Many things are homeostatically regulated by the body, and one of them is energy status (how much energy the body has available for use).  Homeostasis of large-scale processes in the body is typically regulated by the brain.

We can divide the factors that determine feeding behavior into two categories, homeostatic and non-homeostatic.  Homeostatic eating is when food intake is driven by a true energy need, as perceived by the brain.  For the most part, this is eating in response to hunger.  Non-homeostatic eating is when food intake is driven by factors other than energy need, such as palatability, habitual meal time, and food cues (e.g. you just walked by a vending machine full of Flamin' Hot Cheetos).

We can divide energy homeostasis into two sub-categories: 1) the system that regulates short-term, meal-to-meal calorie intake, and 2) the system that regulates fat mass, the long-term energy reserve of the human body.  In this post, I'll give an overview of the process that regulates energy homeostasis on a short-term, meal-to-meal basis.

The Satiety System (Short-Term Energy Homeostasis)


The stomach of an adult human has a capacity of 2-4 liters.  In practice, people rarely eat that volume of food.  In fact, most of us feel completely stuffed long before we've reached full stomach capacity.  Why?

Why Do We Eat? A Neurobiological Perspective. Part I

As with all voluntary movements, eating food is an expression of activity in the brain.  The brain integrates various inputs from around the body, and outside the body, and decides whether or not to execute the goal-directed behaviors of food seeking and consumption.  Research has uncovered a lot about how this process works, and in this series I'll give a simplified overview of what scientists have learned about how, and why, the brain decides to eat.

The Gatekeeper of Voluntary Behaviors

Comment Policy

The nature of the Internet is that comments sections are rowdy places.  But ultimately I do have control over my corner of the world, and I intend to exert it to maintain a higher level of information quality and decorum.  Here are my criteria for deciding whether or not a comment will be published:

1. Value.  Comments should be well thought out, and points supported by research or at least solid logic.  Personal anecdotes are welcome as long as they aren't over-interpreted.  Thoughtful questions are also welcome, although I can't guarantee I'll answer them.  As always, anyone is free to disagree with me in a constructive manner, or simply offer a word of support.  
2. Respect.  Comments should be respectful to me and other commenters, and composed in a concise manner.  It isn't difficult to disagree in a respectful way.
3. On topic.  Comments should be at least somewhat relevant to the subject of the post.
4. Full name.  Attaching your full name to a comment means taking responsibility for what you write.  I'll continue to publish anonymous comments if they add value, but I'll be more likely to publish if you include your full name in your screen name, your profile, or at the bottom of your comment.
5. No ads.  I will not publish links to commercial sites that do not add value to the discussion, nor will I publish any other link I find objectionable.

Because I'll be moderating, I've decided to remove the captcha word authentication, which many people found difficult to use.  We'll see how that goes.  Since I have a lot on my plate, and Whole Health Source is a one-man show, I may not always moderate comments in a timely manner.  I apologize in advance for the inconvenience.  

Announcing the Ideal Weight Program

I often receive requests from people asking for my overall perspective on fat loss and health.  I share my opinions here, but they're scattered throughout hundreds of posts, there's a lot I haven't had a chance to write about, and I rarely give practical recommendations.  However, I knew I'd eventually put everything together into a cohesive fat loss program-- it was only a matter of finding the right opportunity.

That opportunity presented itself in 2011 when I met Dan Pardi, a researcher whose work focuses on sleep and food intake, and the CEO of a company called Dan's Plan.  I was immediately impressed by Dan because he stood out as someone with a high level of expertise in sleep and physical activity, as well as someone who has successfully lost a substantial amount of fat and kept it off for several years.

Dan and his team had developed a set of unique and engaging tools for tracking weight, sleep, and physical activity to help people maintain daily mindfulness over the simple fundamentals of health.  These tools are 100 percent free and incredibly easy to use, particularly if you sync them with an electronic scale and step counter.  When synced with these devices, the Dan's Plan website automatically uploads and displays your weight, sleep, and physical activity score, as well as integrating them all into a single user-friendly Health Zone Score that lets you know your overall performance at a glance.  Even if you have no interest in fat loss, I highly recommend using the free tracking tools on the Dan's Plan site-- I do.

In early 2012, Dan approached me about creating a fat loss program for Dan's Plan that incorporates their unique tracking tools.  This struck me as an excellent opportunity to create a diet and lifestyle program that combines sound science with exciting new technology.  Dan and I both brought science to the table, and Dan also brought the perspective gained from working with others to help them lose fat, as well as his own successful fat loss experience.  Dan and I have been working hard on this project, and we're finally ready to launch.

I'm happy to announce the Ideal Weight Program, an effective new system for fat loss and maintenance.

What is the Ideal Weight Program?

The Ideal Weight Program is a unique system for fat loss and maintenance that draws from the latest science on diet, physical activity, sleep, and behavior modification, and pairs it with engaging tools that help you define your goals and meet them.  It keeps you consistently focused on the everyday factors that really matter for fat loss, and gives you the skills you need to make sustainable diet and lifestyle changes.  Based on your own goals and priorities, you can choose one of two diet strategies for the initial fat loss phase:

• The Fat Loss and Sustainable Health (FLASH) diet, an intensive high-protein diet for rapid fat loss.
• The Simple Food Diet, a more flexible diet based on whole, natural foods specifically selected for fat loss.  One important goal of this diet is to teach healthy cooking skills, using recipes and tips provided.

These diets are designed to naturally promote a lower calorie intake and fat loss, without requiring calorie counting.  The Ideal Weight Program also includes important physical activity and sleep components, and explains why these are so critical for fat loss and health.  Dan and I discussed some of the principles underlying the Ideal Weight Program on Chris Kresser's podcast recently.

Here's what you get when you sign up:

• Detailed documents that walk you through the program
• Weight, sleep, and physical activity tracking tools tailored for fat loss
• Simple recipes and cooking tips that work with almost anything in your fridge
• Videos that explain the key concepts behind fat loss and maintenance
• An e-book explaining the scientific rationale behind the program

Signing up for the Ideal Weight Program gives you lifetime access to everything.  We've discounted the initial price, because we want to hear your feedback so that we can continue to improve the program over time.  If you follow the link below, first you'll be prompted to sign up for a basic Dan's Plan account, and once you have your account set up, you'll be able to purchase the Ideal Weight Program:

Ideal Weight Program



Financial disclosure: I will receive a portion of the revenue from the sale of the Ideal Weight Program.  I do not receive revenue from the sale of other products associated with Dan's Plan or the Ideal Weight Program (such as the Fitbit, cooking tools, and other programs).

Food Reward Friday

This week's "winner"... the KFC Double Down sandwich!

Comment Published in Nature

I recently read an opinion piece by Gary Taubes in the scientific journal Nature, titled "Treat Obesity as Physiology, not Physics", in which he promoted NuSI and repeated the statement that obesity research is a "house of cards" because it focuses on calories in/out, at the expense of studying the "hormonal regulatory disorders" underlying obesity (1).  I wrote a letter to the editor in response to Taubes's commentary, which has been published in Nature (2).

I'm used to seeing these kinds of claims in the popular press at this point, but to see it published in a scientific journal is galling (even if it's in the opinion section).  This is the equivalent of a person who has never held an ax telling a group of lumberjacks they need to focus on cutting trees.  It's part of a disturbing trend of popular writers in the low-carb and Paleo world attacking researchers, and even entire fields of research, they have little understanding of.  Of course this only applies to a minority of the community, but this argumentation style smells of desperation and reflects poorly on the community as a whole.

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.

Food Reward Friday

This week's "winner"... the Garbage Plate!!

Appearance on "Ask the Low-Carb Experts" Podcast Postponed

I was scheduled to appear on Jimmy Moore's show "Ask the Low-Carb Experts" this Thursday.  I don't consider myself a low-carb expert, but I do have expertise in obesity and metabolism, and Jimmy had invited me to discuss these topics on his show.

Due to a confluence of events, I've decided that this is not the best time to do the show.  I want to be clear that I don't intend this as a rebuke of Jimmy Moore or his show-- most of my reasons for postponing have nothing to do with Jimmy.  Thanks for your understanding.

Overfeeding and Elevated Insulin

It's commonly accepted in the obesity research community that fat gain causes insulin resistance and an increase in circulating insulin, and that this is a major reason why obese people usually have insulin resistance and high circulating insulin. Part of the rationale is that substantial fat loss by almost any means improves insulin sensitivity and causes circulating insulin to decline, and substantial fat gain from deliberate overfeeding causes insulin sensitivity to decline and circulating insulin to increase.  I recently cited three references to support this contention on another blog, and was challenged, so I decided to revisit these references to make sure I had understood them correctly (1, 2, 3).  Since I took the time to do this, I figured I may as well write it up for my readers, since these studies are quite informative.

Food Reward Friday

This week's "winner"... the Heart Attack Grill's Quadruple Bypass Burger!

Extreme Flu Activity in the US

A friend of mine came down with a nasty flu recently.  I checked Google Flu Trends, and found that flu activity is currently at "intense" levels throughout the US.  This is the highest flu activity Google Flu Trends has recorded in the last six years (image from Google Flu Trends 1/3/12).