Palatability, Satiety and Calorie Intake

WHS reader Paul Hagerty recently sent me a very interesting paper titled "A Satiety Index of Common Foods", by Dr. SHA Holt and colleagues (1).  This paper quantified how full we feel after eating specific foods.  I've been aware of it for a while, but hadn't read it until recently.  They fed volunteers a variety of commonly eaten foods, each in a 240 calorie portion, and measured how full each food made them feel, and how much they ate at a subsequent meal.  Using the results, they calculated a "satiety index", which represents the fullness per calorie of each food, normalized to white bread (white bread arbitrarily set to SI = 100).  So for example, popcorn has a satiety index of 154, meaning it's more filling than white bread per calorie. 

One of the most interesting aspects of the paper is that the investigators measured a variety of food properties (energy density, fat, starch, sugar, fiber, water content, palatability), and then determined which of them explained the SI values most completely.

Read more »

60 Minutes Report on the Flavorist Industry

A reader sent me a link to a recent CBS documentary titled "Tweaking Tastes and Creating Cravings", reported by Morley Safer.

Safer describes the "flavorist" industry, entirely dedicated to crafting irresistible odors for the purpose of selling processed and restaurant food.  They focused on the company Givaudin.  Dr. David Kessler, author of The End of Overeating, makes an appearance near the end.

Here are a few notable quotes:

Read more »

The Case for the Food Reward Hypothesis of Obesity, Part II

In this post, I'll explore whether or not the scientific evidence is consistent with the predictions of the food reward hypothesis, as outlined in the last post.

Before diving in, I'd like to address the critique that the food reward concept is a tautology or relies on circular reasoning (or is not testable/falsifiable).  This critique has no logical basis.  The reward and palatability value of a food is not defined by its effect on energy intake or body fatness.  In the research setting, food reward is measured by the ability of food or food-related stimuli to reinforce or motivate behavior (e.g., 1).  In humans, palatability is measured by having a person taste a food and rate its pleasantness in a standardized, quantifiable manner, or sometimes by looking at brain activity by fMRI or related techniques (2).  In rodents, it is measured by observing stereotyped facial responses to palatable and unpalatable foods, which are similar to those seen in human infants.  It is not a tautology or circular reasoning to say that the reinforcing value or pleasantness of food influences food intake and body fatness. These are quantifiable concepts and as I will explain, their relationship with food intake and body fatness can be, and already has been, tested in a controlled manner. 

1.   Increasing the reward/palatability value of the diet should cause fat gain in animals and humans

Read more »

Humans on a Cafeteria Diet

In the 1970s, as the modern obesity epidemic was just getting started, investigators were searching for new animal models of diet-induced obesity.  They tried all sorts of things, from sugar to various types of fats, but none of them caused obesity as rapidly and reproducibly as desired*.  1976, Anthony Sclafani tried something new, and disarmingly simple, which he called the "supermarket diet": he gave his rats access to a variety of palatable human foods, in addition to standard rodent chow.  They immediately ignored the chow, instead gorging on the palatable food and rapidly becoming obese (1).  Later renamed the "cafeteria diet", it remains the most rapid and effective way of producing dietary obesity and metabolic syndrome in rodents using solid food (2).

Read more »

Simple Food: Thoughts on Practicality

Some people have reacted negatively to the idea of a reduced-reward diet because it strikes them as difficult or unsustainable.  In this post, I'll discuss my thoughts on the practicality and sustainability of this way of eating.  I've also thrown in a few philosophical points about reward and the modern world.
Read more »

Food Reward: a Dominant Factor in Obesity, Part VII

Now that I've explained the importance of food reward to obesity, and you're tired of reading about it, it's time to share my ideas on how to prevent and perhaps reverse fat gain.  First, I want to point out that although food reward is important, it's not the only factor.  Heritable factors (genetics and epigenetics), developmental factors (uterine environment, childhood diet), lifestyle factors (exercise, sleep, stress) and dietary factors besides reward also play a role.  That's why I called this series "a dominant factor in obesity", rather than "the dominant factor in obesity".
Read more »

Food Reward: a Dominant Factor in Obesity, Part I

A Curious Finding

It all started with one little sentence buried in a paper about obese rats. I was reading about how rats become obese when they're given chocolate Ensure, the "meal replacement drink", when I came across this:

...neither [obesity-prone] nor [obesity-resistant] rats will overeat on either vanilla- or strawberry-flavored Ensure.

The only meaningful difference between chocolate, vanilla and strawberry Ensure is the flavor, yet rats eating the chocolate variety overate, rapidly gained fat and became metabolically ill, while rats eating the other flavors didn't (1). Furthermore, the study suggested that the food's flavor determined, in part, what amount of fatness the rats' bodies "defended."

As I explained in previous posts, the human (and rodent) brain regulates the amount of fat the body carries, in a manner similar to how the brain regulates blood pressure, body temperature, blood oxygenation and blood pH (2). That fact, in addition to several other lines of evidence, suggests that obesity probably results from a change in this regulatory system. I refer to the amount of body fat that the brain defends as the "body fat setpoint", however it's clear that the setpoint is dependent on diet and lifestyle factors. The implication of this paper that I could not escape is that a food's flavor influences body fatness and probably the body fat setpoint.

An Introduction to Food Reward

The brain contains a sophisticated system that assigns a value judgment to everything we experience, integrating a vast amount of information into a one-dimensional rating system that labels things from awesome to terrible. This is the system that decides whether we should seek out a particular experience, or avoid it. For example, if you burn yourself each time you touch the burner on your stove, your brain will label that action as bad and it will discourage you from touching it again. On the other hand, if you feel good every time you're cold and put on a sweater, your brain will encourage that behavior. In the psychology literature, this phenomenon is called "reward," and it's critical to survival.

The brain assigns reward to, and seeks out, experiences that it perceives as positive, and discourages behaviors that it views as threatening. Drugs of abuse plug directly into reward pathways, bypassing the external routes that would typically trigger reward. Although this system has been studied most in the context of drug addiction, it evolved to deal with natural environmental stimuli, not drugs.

As food is one of the most important elements of survival, the brain's reward system is highly attuned to food's rewarding properties. The brain uses input from smell, taste, touch, social cues, and numerous signals from the digestive tract* to assign a reward value to foods. Experiments in rats and humans have outlined some of the qualities of food that are inherently rewarding:

• Fat
• Starch
• Sugar
• Salt
• Meatiness (glutamate)
• The absence of bitterness
  
• Certain textures (e.g., soft or liquid calories, crunchy foods)
• Certain aromas (e.g., esters found in many fruits)
• Calorie density ("heavy" food)
  

We are generally born liking the qualities listed above, and aromas and flavors that are associated with these qualities become rewarding over time. For example, beer tastes terrible the first time you drink it because it's bitter, but after you drink it a few times and your brain catches wind that there are calories and a drug in there, it often begins tasting good. The same applies to many vegetables. Children are generally not fond of vegetables, but if you serve them spinach smothered in butter enough times, they'll learn to like it by the time they're adults.

The human brain evolved to deal with a certain range of rewarding experiences. It didn't evolve to constructively manage strong drugs of abuse such as heroin and crack cocaine, which overstimulate reward pathways, leading to the pathological drug seeking behaviors that characterize addiction. These drugs are "superstimuli" that exceed our reward system's normal operating parameters. Over the next few posts, I'll try to convince you that in a similar manner, industrially processed food, which has been professionally crafted to maximize its rewarding properties, is a superstimulus that exceeds the brain's normal operating parameters, leading to an increase in body fatness and other negative consequences.


* Nerves measure stomach distension. A number of of gut-derived paracrine and endocrine signals, including CCK, PYY, ghrelin, GLP-1 and many others potentially participate in food reward sensing, some by acting directly on the brain via the circulation, and others by signaling indirectly via the vagus nerve. More on this later.