Why We Eat (Too Much) Read online

  Once I had done my research I had my answer. Patients liked my way of explaining to them exactly why they were trapped in this condition. How weight is not under conscious control and therefore cannot be manipulated down by dieting. How you should encourage the body to want to be lighter by changing the day-to-day signals it receives. This is the basis of Why We Eat (Too Much).

  I hope that this book will be read by anyone who is interested in controlling their weight, but is tired of dieting. I hope that people who want to fully understand obesity and weight regulation will pick up this book – anyone who has a friend or relative who is struggling with obesity and cannot control it. Finally, I hope that the people in power – the politicians, journalists and (dare I say it?) even doctors – will study this book. It will change your perception of obesity and, maybe, help future generations to avoid the suffering it brings.

  Part One

  * * *

  LESSONS IN ENERGY

  How Our Body Works to Control Weight

  ONE

  Metabology for Beginners

  How Our Weight is Controlled

  Humans talk, write, walk, and love using the same amount of energy per second as a light bulb, a device that does nothing but shine light and get hot. This amazing fact, far from denigrating humans, is a testament to how efficient a human body is. But more importantly, it is a testament to the wondrous complexity of our bodies, which can do so much with so little.

  Peter M. Hoffmann, Life’s Ratchet: How Molecular Machines Extract Order from Chaos (2012)

  I distinctly remember the first class on my first day of medical school. We were issued with starched white coats to cover up our student sweaters and ripped jeans. The superintendent ushered us into a bright neon-lit room, chilled like a walk-in fridge. Along the length of the room were many evenly placed narrow tables, each with a cotton sheet obscuring what lay below. We paired up, took a table each and jokily grappled to get our latex gloves on. One hour later, if you could have observed this group of eighteen-year-olds coming out of their first lesson, you would have noticed several distinct differences from when they walked in. Two of the group needed to be helped out of the room – and did not consider a career in medicine again. The rest of us were ashen-faced. The sheets over each table had hidden a human cadaver. Each one was drained of blood, with a shaven head, the bodies grey in colour and infused with acrid-smelling formalin to preserve them. This was our first lesson: ANATOMY.

  During our anatomy classes of that year, we dissected, and examined, all the different organs that run the body. We learned how each individual part of the body worked to maintain health. The organ systems that we learned about included:

  Cardiology – how the heart and circulation work

  Pulmonology – how the lungs oxygenate our blood

  Gastroenterology – how we digest and absorb food

  Urology – how the kidneys maintain fluid balance in our body

  Endocrinology – how glands and hormones work.

  These systems gave us the grounding to eventually understand the entire workings of the human body and a basis from which to go on and learn about the diseases that affected them. The classes were supposed to cover all the diseases that we would encounter in our future careers as doctors. However, there was one major omission – none of the organ systems that we learned about adequately explained obesity, the condition that would go on to affect a quarter of our patients throughout our careers, and would trigger unprecedented levels of diabetes, blood pressure and heart problems.

  When we took our sharp scalpels in hand and dissected our cadaver, the first layers to be discarded were the skin and fat. These handfuls of human jelly were thrown into bins for later incineration. What we were unaware of at the time was that by getting rid of the fat we were rejecting an important part of the body. Where was the organ that controls our metabolism and appetite; that coordinates and stores our energy reserves? As we busily dissected a lung, a heart or a kidney, this vital organ was in the tissue bin – discarded and ignored.

  Have medical schools now caught up? When I quiz my students on the training they currently receive in order to understand obesity, it remains similar to the curriculum of the 1980s, with only minor changes. Experts in obesity are therefore by definition self-taught, and because of this their views often differ from regular doctors, who still rely on the limited training they received in medical school.

  In this book, we will go to my ‘virtual’ medical school to cover the subject that should be on the curriculum, but sadly remains ignored. So let’s give the subject a brand new medical name: metabology, from the prefix metabo-, for ‘metabolism’, the chemical processes in cells related to energy, and the suffix -logy, meaning ‘the study of’.

  Metabology – the study of appetite and metabolism, of fat storage or fat loss; the study of the energy flows into and out of the body.

  Metabology is simple – there are only two main rules that you need to remember to master it. You know one of these rules already – energy in (food) minus energy out (exercise) equals energy stored (usually fat). But the other rule is less widely understood. It states that our bodies try and maintain a healthy internal environment by a process called negative feedback. This is the way the body works to stop you losing (or gaining) weight too fast. Remember these rules and you will understand obesity and its causes and treatment better than most. You will have a superior understanding of obesity compared with most doctors, and if you have struggled with weight control in the past all those struggles will become much clearer.

  Before we discuss the Two Rules of Metabology in more detail, let’s first take a look at that organ that was thrown away into the incineration bin in the anatomy class – fat. Fat, or adipose tissue as it is known in medical language, is now recognized as one of our vital and life-preserving organs. An organ is defined as being part of a living thing, but separated from other parts, and having a specific function. The specific function of fat is energy regulation. As we will see, fat not only stores energy but also controls how much we use.

  A Light, Insulating Energy Source

  Fat is made up of individual cells called adipocytes. These cells play a critical role in the survival of any mammalian species – from seals to camels to humans. It has three major properties. First, it is light, compared to muscle or bone; therefore it is efficient to carry around. Second, it provides insulation against the cold and therefore prevents too much thermal or heat energy loss to the air, especially in cold climates. Handy if you are a seal enveloped in a thick layer of blubber, swimming around in ice-cold oceans, not so handy if you are a camel in the 40°C heat of the desert – unless of course you store all the fat in one big lump, or hump, and let the rest of the body breathe. Third, it can store large amounts of energy. Fat is an efficient, lightweight, insulating energy source.

  Each fat cell has the unique ability to store energy for times when it may be needed. The more energy it stores, the more bloated it becomes and the more the fat cell expands in size. In the initial process of becoming fatter, you do not grow more fat cells. The number of cells stays the same, but each one becomes swollen with its stored energy, growing to six times its original volume. When there is no more room within the cells, the number of fat cells in the body increases – from an average of 40 billion to over 100 billion in some cases. Unfortunately, if you suck the fat cells out with liposuction (a common, short-term fix performed by plastic surgeons), more and more fat cells are produced to compensate.

  Energy storage is the most important function of fat as an organ. It is critical to have a store of energy to survive in times of famine and food shortage. The brain needs a constant level of glucose (sugar) in the blood to function. When there is no food readily available, this is replenished constantly by our fat cells. In many types of mammals, including man, there does not need to be an actual famine for our fat stores to be called upon. During migrations, fights to defend territory, fights to obtain a mate, the act
of mating, pregnancy and breast-feeding, the amount of energy taken in as food can be reduced even though the amount of energy needed increases. This is when the fat-storage function comes into play. An energy bank in the form of fat, like a fuel tank in a car, is critical to our survival and for our ability to reproduce and raise the next generation.

  You might therefore think that there would be a major evolutionary advantage to having a large energy store. However, it isn’t in your interest to be carrying an oil-tanker’s worth of energy around as this is going to limit your ability to go about your normal survival activities like hunting or running away from hungry predators. So there must be a mechanism to control the size of these fat tanks: fat is very clever, and very efficient, at self-regulation.

  Metabology Rule 1 – Energy Use and Storage

  The first rule to remember is already in the curriculum for medical students. In most people’s opinion, this rule is what defines obesity: it explains, simply and precisely, energy use and storage. But it is this rule that causes so much prejudice against people who struggle with weight control. It is grandly named ‘The First Law of Thermodynamics’ and is used by physicists to calculate the amount of energy stored in any given object – from a rock, to a plant, to an animal (including a human). Its basic premise is: the energy stored in an object equals the amount of energy taken in minus the amount of energy taken out.

  If you want to simplify things, then just think of a human as a box. This box transforms chemical energy from food into heat, movement and thought. The rest is stored.

  (Energy In) – (Energy Out) = Energy Stored

  In humans, the ‘Energy In’ is what we eat – a combination of proteins, fats and carbohydrates. The ‘Energy Out’ part is just as important and is often misunderstood. Often people think that most of the energy they use up comes from how active they are in the daytime and whether they go to the gym or not. This is not the case. Most of the energy that we use does not involve any type of movement. If we were to lie in bed all day and all night we would still use up to 70 per cent of the energy that we normally do – through breathing, heartbeat, temperature control and all our cells’ chemical reactions. The amount of energy that we use to perform these subconscious tasks is called our basal metabolic rate (or BMR). The concept that over two thirds of our daily energy expenditure is not within our conscious control is an important one to grasp when understanding our metabolism – and how we control our weight and why some people develop obesity.

  What about the remaining 30 per cent of the energy that we normally use? This is made up of two parts:

  Passive energy expenditure – the energy that we use to get on with our everyday lives. This can be anything from walking to work, doing the cleaning, moving around the office or doing a hobby. For most of us – those who don’t go to the gym or have a manual job – this will make up almost all of the remaining 30 per cent of energy used.

  Active energy expenditure – this is the amount of energy that we use up when we perform active exercise. For some this could be going to the gym or jogging. For others, such as builders in England, rickshaw drivers in India, or hunters in the African savannah, it could be part of their daily lives. For sedentary people, meaning most of us working in cities, active energy expenditure may just be running for a bus, or climbing a few flights of stairs, and accounts for just 2 or 3 per cent of our total daily energy used.

  Figure 1.1 Energy used per day by sedentary people compared with active people

  FACT BOX

  The sugar energy in the liver needs water to hold it in place; this makes it quite a heavy energy source (water is much heavier than fat). When you go on a very low-calorie diet, the liver’s stores of energy are the first to be used up. As the sugar in the liver is used, so the water is flushed out and hey presto you think that you have lost a lot of weight in a few days – but it is mostly water and not fat. This is one of the main tricks that fad diets play on people: you think you are making real progress with initial weight loss but it is mainly fluid and the weight loss is transient.

  The ‘Energy Stored’ part of the equation is simpler. Any excess energy is stored first in the liver (as a type of sugar) and then in fat cells (as fat). The liver can only hold a couple of days’ worth of energy; it is generally full to capacity, so in practice excess energy is usually stored in fat. The energy in fat can help keep us going for about thirty days without food. Knowing this takes us on to the rule that is almost always overlooked when explaining obesity.

  Metabology Rule 2 – Negative Feedback System

  The second rule is called the negative feedback system. You may wonder, isn’t that what I get from the boss when he catches me coming into work late? And yes, in a way you would be correct. Negative feedback describes the regulation of a system: it can be an office system or a mechanical system (like a machine) or a biological system (like that of a human). The system has a set way of working (like nine-to-five office hours) and if it senses the way of working deviates from the set rule, then it will automatically correct itself.

  Negative feedback systems are simple. They just need a sensor connected to a switch which changes the system back to where it should be. In our office example, the boss is the sensor to your late arrival and his warning is the switch to change your future behaviour.

  An example of this in a machine would be a household thermostat. It is designed to maintain a set temperature. It senses when the temperature in the house falls below this and switches on the central heating. When the temperature then exceeds the setting, it automatically turns the heating off.

  In the organ systems we explored in medical school we saw many examples of biological negative feedback. These are protective mechanisms that keep us on an even keel (in medical language this is called homeostasis). It means that harmful changes are sensed and automatically counteracted – the reason for negative feedback is to maintain order and health. Let’s demonstrate a couple of examples in humans. For us to function efficiently we need to be at the correct temperature and have the correct proportion of water in our bodies. Here’s how negative feedback works to automatically regulate this.

  Sweltering (Drip) … or F-F-F-Freezing

  It is essential that we keep our own body temperature at around 37 °C. All the chemical reactions in our bodies rely on thermal motion (the continuous movement of our atoms) at a particular rate. This rate is set by our temperature. If our temperature goes up to 40 °C, then we get heatstroke; if it goes down to 35 °C we develop hypothermia.

  Our own internal thermostat tries to control our body temperature to within quite a narrow range. We have all experienced getting too hot or too cold. What happens? Sensor says too hot: switch on coolant mode and start to sweat (when the sweat evaporates it cools the body by taking heat). Sensor says too cold: switch on heating mode and start to shiver (the muscular activity of shivering produces internal body heat).

  Thirsty?

  Another example of negative feedback is our hydration system. Once we understand how our body regulates its water content, it becomes easy to understand how it also regulates its energy content, and therefore how much fat is stored – the hydration and energy storage systems are similar. All doctors know how we regulate water in our bodies – this is taught in medical school – but I imagine that only a minority of them grasp energy regulation.

  Let’s look at the hydration system. This negative feedback system has one sensor connected to two switches. Water makes up 70 per cent of our bodies. Beneath our skin, we are basically immersed in a 37 °C salt-bath. We need to make sure the water in our bodies is not too concentrated or diluted. If we become over-hydrated it can lead to seizures (and eventual death), and if we become too dehydrated we become weak and dizzy (and also, in severe cases, die).

  The Sensor – the Kidney

  The sensor to detect dehydration or over-hydration in the blood is in the kidney. Once it senses a change it secretes a hormone (called renin) which leads to a message b
eing sent to the two switches. The two switches control:

  The amount of water we take in – by controlling our thirst

  The amount of water we let out – by controlling how much urine we make.

  We Only Need 700cc But are Thirsty for More

  The kidneys need to purify the blood of waste (urea) by producing urine. They can do this by producing just 700cc per day.fn1 If we excrete below this volume of urine, we become unwell and start to develop kidney failure, so the kidneys signal for us to drink about double the minimum amount of water needed for health. We therefore drink about 1.5 litres of water per day and produce the same amount of urine. We don’t need to drink 1.5 litres – we could survive on about 700ml per day – but as an insurance mechanism our thirst switch is ratcheted up so that we have plenty of essential water going through our system.

  Biological systems like to be on the safe side, so, in this case, they habituate us to drink much more water than needed. Biology likes a safety buffer – this is an important point to remember when we compare our water-regulating system to our energy-regulating system. If we go without anything to drink for a few hours, then the kidney senses this. It sends a signal to turn on the switch located in the brain that controls thirst – the water-in switch. The brain gets the thirst signal and all you can think about is getting water. The more dehydrated you are, the stronger the thirst signal. At the same time the kidney sends a signal to turn off the water-out switch. We then produce only the minimal amount of concentrated, dark urine – less water is excreted and more is retained. Dehydration fixed.