The Obesity Riddle

By 2015, the year in which the Millennium Development Goals will come to an end, it is estimated that worldwide, one in every third persons will be overweight and one in ten will be obese. Staggering statistics yes? Why is this happening? Riddle me this, riddle me that, who’s afraid of this thing called fat? Be afraid, be very afraid.

First, some definitions

Overweight versus Obesity. Often two words that are intertwined and confused but their differences are significant. As can be assumed, if you are overweight, you are well on your way to becoming obese. Overweight and obesity are defined as abnormal or excessive fat accumulation that presents a risk for a number of chronic diseases, including diabetes, cardiovascular diseases and cancer. Once considered a problem only in high income countries, overweight and obesity are now dramatically on the rise in low- and middle-income countries, particularly in urban settings.

  • Overweight is defined as having an adult with a body mass index (BMI) between 25 and 29.9.
  • Obesity is defined as an adult who has a BMI of 30 or higher.

BMI is a person’s weight in kilograms divided by the square of his or her height in meters. BMI correlates with body fat but doesn’t directly measure body fat, so take the measure as a proxy, not the end all, be all of body fat measures.

Second, some statistics:

  • Overall, more than one in ten of the world’s adult population was obese.
  • Worldwide obesity has more than doubled since 1980.
  • More than 1.4 billion adults, 20 and older, were overweight. Of these, over 200 million men and nearly 300 million women were obese.
  • 65% of the world’s population live in countries where overweight and obesity kills more people than underweight.
  • More than 40 million children under the age of five were overweight in 2010.
  • Overweight and obesity are the fifth leading risk for global deaths. At least 2.8 million adults die each year as a result of being overweight or obese.
  • 44% of the diabetes burden, 23% of the ischaemic heart disease burden and between 7% and 41% of certain cancer burdens are attributable to overweight and obesity.
  • Once considered a high-income country problem, overweight and obesity are now on the rise in low- and middle-income countries, particularly in urban settings. Close to 35 million overweight children are living in developing countries and 8 million in developed countries.


So, back to our riddle. Why are there so many overweight and obese people in the world? There are multiple theories and hypotheses in which I explore in more detail.

Theory #1:  Calorie in = Calories out

The idea is, if you eat more, you will gain more weight. If you eat less, you will lose weight. It is a simple energy imbalance with food energy intake as measured in kilocalories per day exceeding total energy expenditure or exceeding what the body needs in energy to live and function in a healthy way.

Theory #2: Lack of physical activity

Modern populations lead a more sedentary lifestyle due to modernization and mechanization of activities, and lower energy expenditure. We don’t do backbreaking agriculture in the Western world, and do not hunt for our food. We sit in front of monitors all day, ride in cars, and take elevators and escalators to get to where we need to go. The idea is, if you don’t exercise, you don’t expend calories. You also lose muscle mass, which is less metabolically active.  Some researchers put forth the theory that the physical activity-rest cycle is just as important as the feast-famine cycle that occurs in hunter-gatherer populations. In the hunter-gatherer society, food was obtained through rigorous physical activity. However, a recent review of studies looking at exercise and body composition changes, showed that weight loss, resulting from an exercise intervention, was lower than hoped and predicted. The main reason for this was due low energy expenditures during exercise and increases in caloric intake. Shwwoopsies! More on this in a moment…

Theory #3: Thrifty gene hypothesis

The idea of this hypothesis is that evolution has shaped the genetic profile of humans so as to cope with hardship. Some of the world’s populations are genetically adapted to an environment in which calories are scarce. As a result, their bodies are unable to cope in times of overindulgence and it takes only a small increase in daily calories to tip the scales. And the world is now inundated with the “Western diet” composed of energy dense foods, particularly high processed foods that contain trans fats, high fructose corn syrup and simple sugars that increase adiposity. Many of these foods and this type of diet is cheap, readily available in urban settings, and in the developing world. We even find these foods very accessible in food deserts – poor urban dense areas like slums in India, and literally, deserts, where native American reservations are, and Aboriginal populations in Australia. Some of these populations, such as South Asian Indians have massive burdens of NCDs, like diabetes.

Public health: India’s diabetes time bomb: Priya Shetty; Nature 485, S14–S16

This hypothesis was introduced in 1962 by James Neel to explain why some ethnic groups tend to have higher risk towards obesity and diabetes. It is assumed that certain genes in humans have evolved to maximize metabolic efficiency and in times of abundance, these genes predispose them to diseases due to excess nutrient intake. The problem with all this is that no genes have been specifically identified. Hmmm…just a small problem. You can read Neel’s paper here. In Neel’s hypothesis, he stated that ancient humans went through cycles of feasts followed by famines. Those who were better able to store energy were more likely to survive during those famine times and their genes were selected over time, as the most efficient in fuel utilization and storage. However over millennia, the transition to overnutrition, food abundance and sedentary lifestyles, that thrifty gene has turned against us. Drats.

Case study: A recent study examined all three of our first theories by measuring the daily energy expenditure and physical activity level of the Hadza foragers. They are considered modern day hunter-gatherers living in a savannah-woodland environment in Tanzania. They are very similar to our ancestral hunter gatherer, Pleistocene types. They hunt game and gather plants and honey by foot, with bows and small axes. Ninety five percent of their diet comes from wild foods. Amazing yes?

Their energy expenditure and body composition was measured. Now, you would think they would definitely expend more energy and you would think that body composition wise, they would be leaner, have less body fat and more muscle. Although they did have great physical activity as compared to Westerners, and they were overall lean with body fat percentages on the low end of healthy range for Western populations, like 20% for Hadza women compared to 38% for western women (and 27% for farming women) for example, their total energy expenditure was the similar to Western populations for both men and women!

nergy expenditure for Hadza hunter-gatherers (red circles) was similar to that of Westerners (gray). Bolivian women farmers (blue open circles) had higher TEE than either Hadza or Western women.

This is counterintuitive due to their higher physical activity levels. Even dramatic differences in lifestyles may have a negligible effect on energy expenditure and perhaps obesity is more dependent on energy intake rather than expenditure. Thus traditional lifestyles may not protect against obesity if diets change to promote increased caloric consumption. This supports some theories of the Aboriginies in Australia, Native American Indians, and South Indian populations who are active, but also have high burdens of diabetes.

This study supports the notion that Paleolithic humans who were very acive hunter-gatherers, have very similar daily energy requirements to modern Western populations. As the authors stated: “Perhaps total energy expenditure is a stable trait in human species as the study suggests, more than environmental influences, ie “species metabolic rates reflect their evolutionary history.”

Theory #4: Epigenetics or thrifty phenotype

It all begins with our mamas. Also known as the “early life nutrition programming.” This is a theory introduced by a bloke named Robert Barker. The idea is when an individual is deprived of nutrients in the womb and then exposed to high calorie, low exercise lifestyle later, the person is more susceptible to putting on pounds and being at risk for non-communicable diseases (NCDs) like diabetes, stroke and heart disease. This explains why we are seeing so much obesity and NCDs in the developing world. Epigenetics describes the relationship between the environment and genetic background to produce a phenotypic outcome. It is the temporal, spatial control of gene activity in individuals – the fetal environment triggers changes in DNA coding that switches genes on or off. The environment in utero thereby effects the expression of genes. Thus, a mother’s nutrition, habits and exposures in the environment can shape the genetic coding of her unborn child. This prenatal nutrition/genetic link is being shown to hold true through large scale studies.

Many studies are now underway to determine the genetic and environmental mechanisms of how programming, imprinting (no not the Twilight werewolf type of imprinting) and interactions occur from maternal (mal)nutrition to fetus and its repercussions into adulthood.

Theory #5: The bad macronutrient

Fat was once to blame for all the obesity in the world, much like the Riddler of Gotham city, but now, its carbohydrates. The Atkins diet, South Beach diet and authors like Gary Taubes have found a way to villanize carbohydrates, much in the way that the food industry basically outlawed fat in the 1980s. I am not saying the proof isn’t there, as there is a case as of to why simple sugars have wreaked havoc on our systems, but eliminated major food groups or a macronutrient, carbohydrates, from the diet is silly. Funny how everyone has a gluten allergy these days…Just like we were all lactose intolerant 10 years ago. Eliminating wheat from your diet won’t help you lose those 20 pounds honey, just like eliminating dairy didn’t. It ain’t that simple. Sorry…

A ketosis diet is low carbohydrate, high fat and moderate protein intake. This type of diet puts you into ketosis, a metabolic condition where your body burns fat for energy rather than carbohydrates, its normal energy source. This is not the first choice or optimal for the brain. But who needs to think?

Many argue that this diet is the best as it taps into our hunter gatherer state. Paleolithic ancestors were carnivores, dominated by fats and proteins and very few carbs. It wasn’t until about 10,000 years ago that modern humans developed a lifestyle based on the staple crops found in agriculture systems today. Some argue that the Inuit have low risk of heart disease due to their rich fat and protein diet – usually 85% fat and 15% protein, and little carbohydrate. But not sure we can all eat whale blubber on a daily basis. Remember saving our whales? Oh, and the Massai, who eat blood, milk and meat from their livestock. Ummmm…unless you plan to walk 50 kilometers a day as a pastoralist across the great Rift Valley, that may not be a viable option either.

According to one dietitian: “When an individual with normal insulin response ingests carbohydrates and absorbs it as glucose, the hormone insulin is released. Insulin facilitates glucose uptake into the body’s muscles where it can be stored as glycogen or burned as fuel. In a person who is insulin resistant, the insulin can’t do its job as effectively and the carbohydrates are instead routed to the liver, where it is converted to fat.” But dude, not all of us our insulin resistant…so, there goes that textbook theory.

This theory goes back to first theory: is a calorie just a calorie? We know one gram of carbohydrate is 4 calories, as is protein, whereas 1 gram of fat is 9 calories. Is it all that simple? According to Dr. Jules Hirsch, emeritus professor and emeritus physician in chief at Rockefeller University, one of the leading obesity researchers in the world:

“Perhaps the most important illusion is the belief that a calorie is not a calorie but depends on how much carbohydrates a person eats. There is an inflexible law of physics — energy taken in must exactly equal the number of calories leaving the system when fat storage is unchanged. Calories leave the system when food is used to fuel the body. To lower fat content — reduce obesity — one must reduce calories taken in, or increase the output by increasing activity, or both. This is true whether calories come from pumpkins or peanuts or pâté de foie gras. To believe otherwise is to believe we can find a really good perpetual motion machine to solve our energy problems. It won’t work, and neither will changing the source of calories permit us to disobey the laws of science.”


A recent study in Jama, showed that among overweight and obese young adults, those on very low carbohydrate diets, (ala Atkins diet) lost the most weight and had increased total energy expenditure. Dr. Hirsch said about the results:

“They report that people on the Atkins diet were burning off more calories. Ergo, the diet is a good thing. Such low-carbohydrate diets usually give a more rapid initial weight loss than diets with the same amount of calories but with more carbohydrates. But when carbohydrate levels are low in a diet and fat content is high, people lose water. That can confuse attempts to measure energy output. The usual measurement is calories per unit of lean body mass — the part of the body that is not made up of fat. When water is lost, lean body mass goes down, and so calories per unit of lean body mass go up. It’s just arithmetic. There is no hocus-pocus, no advantage to the dieters. Only water, no fat, has been lost.”


Did we solve the riddle? Maybe not but keep your eye out on the epigenetics front because the hand that rocks the cradle is the hand that rules the world. And as the old saying goes: nothing comes easy. Eat less, exercise more, and hope that your mama treated you right. Let’s end on some James Brown, just because we can. Mother, she got to have…some mother popcorn for ya.




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One Response to The Obesity Riddle

  1. Pingback: Potato chips are really bad for you. Sad… | You Are What You Eat

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