There are numerous theories as to the cause of obesity, today I will discuss two of which I have been reading a lot about recently.
Food reward/palatability theory
This is a theory that is based around the notion that obesity is driven by food reward and/or food palatability. When talking about this what we mean by reward is a process that reinforces behavior, therefore food reward is ‘the process by which eating specific foods reinforces behaviors that favor the acquisition and consumption of the food in question.’
This reward factor can be broken up into simple parts, the taste, smell, texture, calorie content etc of the food and how it affects the brain (everyone loves the sugar kick right?). If the brain perceives something as positive, enjoyable, tasty etc it is going to seek out that reproduce that feeling. On the flip side if you experience something negative (like scalding you hand under a hot tap) your brain will soon learn how to avoid that situation again. It is thought that as food and its consumption is vital to survival the brain places high importance on food reward. Our brains are believed to have evolved to differentiate between positive and negative experiences and the stimuli associated to them, however when these pathways are over stimulated (heroin, cocaine…sugar?) then it leads to what we have come to know as addiction, so it is suggested that sugar and other food stuffs can literally be addictive.
Food manufactures caught on to this idea a good while back and have been exploiting it (and the public) ever since. Manufactures of food items are in competition with each other to sell more products and make ever bigger revenues, in order to do that they need to sell more. To get people to keep buying their product over a rivals they have produce something that you will repeatedly purchase. ‘…the goal of processed food manufacturers is to create a product that maximally reinforces purchase and consumption behaviors– food reward! If the product is not extremely rewarding, it won’t sell because it’s competing against other products that are extremely rewarding. Only the most rewarding products survive.” We all know which products have that reward factor, it certainly isn’t the cabbage and carrots, its the processed junk food like cakes, chocolate, crisps and cookies.
Check out these interesting studies, in this first one the researchers gave one group of rats free access to foods from their normal diets and ‘junk’ foods that were considered both rewarding and palatable. Its no surprise this group of rats soon stopped eating their regular diet, ate the junk food and became obese.
This second study was done on humans and the researchers managed to make obese people lean. They did this by offering them unlimited access to food, however this food was in the form of a bland, tasteless liquid. They concluded that as the food had a low reward/palatability factor that the subjects consumed only enough to feel satiated and so did not overeat.
This is a theory we are more familiar with, the idea that consuming carbohydrate heavy, processed, sugar rich foods cause a large increase in our insulin levels (insulin is a storage hormone which tells our cells to store energy). This is a normal process but it is thought that overeating these foods can upset the system causing weight gain.
When we have a meal the level of glucose in our blood increases, in order to get this back to a normal level our body releases insulin. This hormone tells our cells to take up the excess glucose where it will either be used as energy or stored as glycogen, when glycogen stores are full it gets converted to fat instead.
If we eat a particularly high carbohydrate meal (or some sugary treats!) we have a sudden and rather large increases in blood sugar and so we release a sizable amount of insulin to combat this. However the overload of insulin causes our cells to essentially be vacuums and take as much glucose out the bloodstream as possible, this causes a sudden drop in blood glucose which our brain notices (and we notice as fatigue or lethargy), this is commonly called the sugar crash. As a result the brain stimulates our appetite as it believes we are short of energy and so we eat more carbohydrates and the cycle continues.
In overweight/obese people this process is out of control. The chronically elevated insulin levels has destroyed the insulin receptors on the cells therefore the cells dont respond as well to ‘normal’ levels of insulin. In order to get rid of the rising level of blood glucose our body just releases even more insulin leading to further insulin resistance. When this happens obese people who are metabolically deranged often feel hungry the majority of the time as there cells are constantly being told to take up the glucose and store it, if not enough is left in the blood stream to use for energy our brain thinks we are starving and tells us to eat more, and the cycle perpetuates until the individual in question either dies from a whole range of related diseases, or gets a handle on the problem.
So which is correct?
What seems strange to me is that most people appear to sit either side of the fence on this topic, its either this theory or that theory. To me these competing theories could go hand in hand, we have a food reward factor where individuals reinforce the behavior of eating foods that promote good feelings to which the brain seeks out to reproduce. We all know which food stuffs tend to give us these feelings, the high carb, processed sugary foods right? So we are constantly seeking out to eat these foods that cause the chronic over secretion of insulin which leads to disregulated fat/energy metabolism. Its a very simplistic piece of logic and granted its a little more complex than I make it sound, as ever there is research out there that both supports and contradicts both theories as well as a number of other possible explanations as to the cause of weight gain and obesity.
Here are two more AHS talks, the first is Stephen Guyenet of the food reward/palatability theory, the second is Gary Taubes of the Carbohydrate theory of obesity (these two have a bit of a feisty Q&A at the end of Stephens talk!)
What ive been eating this week:
Lime Grilled Chicken
What I’ve been reading this week:
Workout of the day
A: Build to a max height box jump in 10 minutes
B: 3 rounds for time of:
10 Deadlift 120/85kg
50 Double unders