Nature Genetics just published a paper that caught my interest (1). Investigators reviewed the studies that have attempted to determine associations between genetic variants and common obesity (as judged by body mass index or BMI). In other words, they looked for "genes" that are suspected to make people fat.
There are a number of gene variants that associate with an increased or decreased risk of obesity. These fall into two categories: rare single-gene mutations that cause dramatic obesity, and common variants that are estimated to have a very small impact on body fatness. The former category cannot account for common obesity because it is far too rare, and the latter probably cannot account for it either because it has too little impact
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Tuesday 30 November 2010
The Twinkie Diet for Fat Loss
The Experiment
I've received several e-mails from readers about a recent experiment by nutrition professor Mark Haub at Kansas State university (thanks to Josh and others). He ate a calorie-restricted diet in which 2/3 of his calories came from junk food: Twinkies, Hostess and Little Debbie cakes, Dorito corn chips and sweetened cereals (1). On this calorie-restricted junk food diet (800 calorie/day deficit), he lost 27 pounds in two months.
Therefore, junk food doesn't cause fat gain and the only thing that determines body fatness is how much you eat and exercise. Right?
Discussion
Let's start with a few things most people can agree on. If you don't eat any food at all, you will lose fat mass. If you voluntarily force-feed yourself with a large excess of food, you will gain fat mass, whether the excess comes from carbohydrate or fat (2). So calories obviously have something to do with fat mass.
But of course, the situation is much more subtle in real life. Since a pound of body fat contains roughly 3,500 calories, eating an excess of 80 calories per day (1 piece of toast) should lead to a weight gain of 8 lbs of fat per year. Conversely, if you're distracted and forget to eat your toast, you should lose 8 lbs of fat per year, which would eventually be dangerous for a lean person. That's why we all record every crumb of food we eat, determine its exact calorie content, and match that intake precisely with our energy expenditure to maintain a stable weight.
Oh wait, we don't do that? Then how do so many people maintain a stable weight over years and decades? And how do wild animals maintain a stable body fat percentage (except when preparing for hibernation) even in the face of food surpluses? How do lab rats and mice fed a whole food diet maintain a stable body fat percentage in the face of literally unlimited food, when they're in a small cage with practically nothing to do but eat?
The answer is that the body isn't stupid. Over hundreds of millions of years, we've evolved sophisticated systems that maintain "energy homeostasis". In other words, these systems act to regulate fat mass and keep it within the optimal range. The evolutionary pressures operating here are obvious: too little fat mass, and an organism will be susceptible to starvation; too much, and an organism will be less agile and less efficient at locomotion and reproduction. Energy homeostasis is such a basic part of survival that even the simplest organisms regulate it.
Not only is it clear that we have an energy homeostasis system, we even know a thing or two about how it works. Early studies showed that lesioning a part of the brain called the ventromedial hypothalamus causes massive obesity (3; this is also true in humans, when a disruption results from cancer). Investigators also discovered several genetic mutations in rats and mice that result in massive obesity
View the Original article
I've received several e-mails from readers about a recent experiment by nutrition professor Mark Haub at Kansas State university (thanks to Josh and others). He ate a calorie-restricted diet in which 2/3 of his calories came from junk food: Twinkies, Hostess and Little Debbie cakes, Dorito corn chips and sweetened cereals (1). On this calorie-restricted junk food diet (800 calorie/day deficit), he lost 27 pounds in two months.
Therefore, junk food doesn't cause fat gain and the only thing that determines body fatness is how much you eat and exercise. Right?
Discussion
Let's start with a few things most people can agree on. If you don't eat any food at all, you will lose fat mass. If you voluntarily force-feed yourself with a large excess of food, you will gain fat mass, whether the excess comes from carbohydrate or fat (2). So calories obviously have something to do with fat mass.
But of course, the situation is much more subtle in real life. Since a pound of body fat contains roughly 3,500 calories, eating an excess of 80 calories per day (1 piece of toast) should lead to a weight gain of 8 lbs of fat per year. Conversely, if you're distracted and forget to eat your toast, you should lose 8 lbs of fat per year, which would eventually be dangerous for a lean person. That's why we all record every crumb of food we eat, determine its exact calorie content, and match that intake precisely with our energy expenditure to maintain a stable weight.
Oh wait, we don't do that? Then how do so many people maintain a stable weight over years and decades? And how do wild animals maintain a stable body fat percentage (except when preparing for hibernation) even in the face of food surpluses? How do lab rats and mice fed a whole food diet maintain a stable body fat percentage in the face of literally unlimited food, when they're in a small cage with practically nothing to do but eat?
The answer is that the body isn't stupid. Over hundreds of millions of years, we've evolved sophisticated systems that maintain "energy homeostasis". In other words, these systems act to regulate fat mass and keep it within the optimal range. The evolutionary pressures operating here are obvious: too little fat mass, and an organism will be susceptible to starvation; too much, and an organism will be less agile and less efficient at locomotion and reproduction. Energy homeostasis is such a basic part of survival that even the simplest organisms regulate it.
Not only is it clear that we have an energy homeostasis system, we even know a thing or two about how it works. Early studies showed that lesioning a part of the brain called the ventromedial hypothalamus causes massive obesity (3; this is also true in humans, when a disruption results from cancer). Investigators also discovered several genetic mutations in rats and mice that result in massive obesity
View the Original article
Monday 29 November 2010
Impressions from the Wise Traditions Conference
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Glucose Tolerance in Non-industrial Cultures
Background
Glucose is the predominant blood sugar and one of the body's two main fuel sources (the other is fatty acids). Glucose, in one form or another, is also the main form of digestible dietary carbohydrate in nearly all human diets. Starch is made of long chains of glucose molecules, which are rapidly liberated and absorbed during digestion. Sucrose, or table sugar, is made of one glucose and one fructose molecule, which are separated before absorption.
Blood glucose is essential for life, but it can also be damaging if there is too much of it. Therefore, the body tries to keep it within a relatively tight range. Normal fasting glucose is roughly between 70 and 90 mg/dL
View the Original article
Glucose is the predominant blood sugar and one of the body's two main fuel sources (the other is fatty acids). Glucose, in one form or another, is also the main form of digestible dietary carbohydrate in nearly all human diets. Starch is made of long chains of glucose molecules, which are rapidly liberated and absorbed during digestion. Sucrose, or table sugar, is made of one glucose and one fructose molecule, which are separated before absorption.
Blood glucose is essential for life, but it can also be damaging if there is too much of it. Therefore, the body tries to keep it within a relatively tight range. Normal fasting glucose is roughly between 70 and 90 mg/dL
View the Original article
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