This is an example of weight loss by reducing your weight set-point. Weight loss by changing your habits and environment (e.g. walking to work, doing a sports class or going to the gym a couple of times a week), and therefore changing the signals that you are sending to your weight-control centre, is the only way to successful, sustained weight loss. If you talk to anyone who has lost weight and, more importantly, managed to maintain their weight loss over a long period of time, you will see that they have done this by altering their daily habits and thereby lowering their weight set-point. We discuss practical ways to reduce the weight set-point in Part Three of this book.
New Diet or New Life?
If we compare two people who have lost 10kg in weight – one from low-calorie dieting and one from lowering their weight set-point by lifestyle changes – we can see two different people.
The low-calorie dieter may reach their target weight loss much more quickly than the lifestyle changer, but their weight set-point will not have changed; in fact, it could be slightly higher because of the diet. It would be more and more difficult for the dieter to maintain the weight loss over time. In contrast, the lifestyle changer would have a weight set-point matching their weight. The weight loss would have taken considerably longer, but it would be sustainable – in fact, it might get easier over time, as fitness and metabolism increased.
10kg (1½ stone) weight loss
By dieting By set-point
Metabolic rate Decreased Increased
Appetite Increased Normal
Satiety Decreased Normal
Fatigue Yes No
Quality of life Poor Great
Long-term outcome Weight regain to higher level than before diet Sustained weight loss
Table 12.1 Comparison of two people who have lost 10kg – one through dieting; the other by adjusting their weight set-point
What about the commonly used diets? How might they affect our weight set-point?
Low-Calorie Diets
LighterLife, the Cambridge Weight Plan and the SlimFast diet are all examples of very low-calorie diets (600–1,200kcal/day). These types of diets generally use meal-replacement shakes, soups and low-calorie snack bars (which you have to buy from the company) and therefore by definition are not sustainable in the long term if you want to have a good quality of life (i.e. be able to eat). We have discussed the metabolic changes that occur after low-calorie diets. In the long run they raise your set-point, meaning that when you come off the diet you will regain all your lost weight and then some more until your new weight set-point is reached.
Low-Fat Diets
Slimming World’s regime is based on a low-fat diet. It does not restrict the amount of food that you can eat but advises you to replace high-fat foods with lower-fat, filling foods. It is based on the flawed assumption that fat makes you fat (see chapter 11) and separates foods into three categories: Free Foods, Healthy Extras and Syns. Free Foods are, as the name implies, free to eat, in unlimited quantities. These include vegetables, lean meat and fruits. But they also include unlimited carbohydrates in the form of pasta and rice. They advise limited amounts of Healthy Extras, including dairy products and also cereals and bread. The Syns are ‘treat’ foods, like biscuits and chocolate. Between five and fifteen Syns can be taken every day.
The benefits of Slimming World’s diet as far as the set-point is concerned are that it encourages home cooking and the consumption of more natural foods. The drawbacks are that people may switch to a much higher carbohydrate content of the food consumed to the detriment of their insulin profile. All in all, dieters who succeed using Slimming World’s diet are probably cutting down on ultra-refined carbs (contained in the Syns), and this helps lower the weight set-point slightly.
Low-Carb Diets
The Atkins, Paleo and Dukan diets are based on low-carb eating. Once carbohydrate intake is reduced to under 20 grams per day, a process called ketogenesis occurs.
There are many celebrity advocates of ketogenic dieting, such as LeBron James, Kim Kardashian and Halle Berry. I think it is an effective way of reducing weight, but it has a catch: very unpleasant side effects, anything from a pounding headache to profound weakness, constipation, nausea and vomiting (at least you’re not hungry) to flu-like symptoms. The aim of the ketogenic diet is to starve your body of carbohydrates so that it has to use up its own stores. By not taking in any food that can be broken down into glucose, you are forcing your body to start using the reserve that is stored in the liver.
So far, we have concentrated on fat as the main store of energy in the body. In chapter 1 we mentioned that the liver also acts as an energy store. In times of starvation (or dieting), or just at times when we are using lots of energy and not taking in much (such as running marathons), the first place the body goes for easy and quick energy is the liver. We have two to three days’ store of energy there. As we mentioned previously, the glucose that is stored in the liver needs to be surrounded by water and therefore this is quite a heavy source of energy compared to fat. The initial weight loss of any calorie-restriction diet is from these stores of glucose in the liver. As this energy is used up, so the water in the liver required to hold it in place is lost. The result? Lots of initial weight loss – but none of it is fat.
When trying to understand these two sources of our energy (fat and liver), imagine the human body as like a hybrid car. The hybrid car runs most of the time on its battery (in the human body it’s the liver), but when the charge is running low it will switch to using the petrol tank for energy. In a similar way, in our day-to-day tasks we rely on our liver to provide our main source of energy. When the liver is running low, we are forced to switch to our other source of energy, our fat (the fuel tank). Advocates of the ketogenic diet run their hybrid energy bodies on an empty liver (a flat battery). When the liver is ‘empty’, the whole engine (human body) runs less efficiently and therefore it’s easier to run down the tank (and lose weight).
There is another major drawback with the ketogenic diet, though – you have to remain on it for life if you are going to maintain the weight loss. This can be difficult in view of the extreme side effects and also because of the real difficulty of finding nutritious foods on the high street that have almost no carbs. When the ketogenic dieter’s battery (liver glucose) is running on empty and they are ‘burning’ fat, they can sense this because their brain is forced to use a type of fuel called ketone bodies for its energy. Many followers of this diet say that this alternative brain fuel makes them feel more alert, and helps them think more clearly. Thinking fast and clearly would presumably have been an evolutionary survival advantage for our ancestors when they found themselves in an environment where food was scarce.
The ketogenic diet is so extreme in terms of its side effects, and the difficulty of finding the correct foods, that advocates have to be very determined. Presumably they get used to running on empty and love the buzz that it gives them. I personally would not advise anyone to try it. As with the majority of diets we’ve looked at in this book, if you lost a lot of weight dieting this way, and then reverted to eating more normally again, you would regain all of that lost weight … and more.
Intermittent Fasting
Popular examples of intermittent fasting are the 5:2 diet and the 16/8 diet. The 5:2 diet involves eating normally for five days of the week, and for two non-consecutive days limiting calorie intake to 500 or 600kcal. The 16/8 diet advocates eating only during an eight-hour window in the day and then consuming only tea, coffee and water for the remaining sixteen hours. This can easily be done by skipping either breakfast or a late evening meal. Both of the diets advise the need to consume healthy foods and avoid processed or fast foods.
Unlike many other types of diets, intermittent fasting, just like low-carb dieting, remains popular – which means that it probably does work for some people. Old-fashioned, conventional thinking would suggest that by fasting for long periods of time, or by cutting out meals, the number of calories consumed is
decreased and therefore by using the energy in/energy out equation weight is lost. But we now know that sustained weight loss does not occur by simple calorie restriction. So how does this diet work? By decreasing the opportunities for eating, and at the same time by asking followers of the diet to avoid processed and junk foods, both the insulin profile and the omega ratio of the dieter will be improved and therefore the weight set-point will be reduced.
Vegetarian and Vegan Diets
Many advocates of vegetarian and vegan diets do so out of concern for the environment and animal welfare, but are they a reliable way of losing weight? Two of the main causes of an elevated set-point (and therefore weight gain) discussed in this book are an unnaturally high insulin profile and a relative deficiency of omega-3 compared to omega-6 essential fatty acids in our food. We know that some nomadic tribes, such as the Maasai, consume meat, blood and milk – a carnivorous diet. These tribes avoid sugar, carbohydrates and artificial oils in their diet and therefore avoid weight gain and obesity. What about the opposite to the carnivorous diet? How does avoiding animal products affect these risks?
Most vegetarians and vegans will eschew many types of processed foods because they contain animal products. This will have a positive effect on both the amount of sugar and the amount of omega-6 oils that they take in. However, most will be unaware that frying foods in vegetable oils, and consuming nuts and seeds (all very high in omega-6), will have a detrimental effect on their omega profile, particularly as a valuable source of omega-3 in fish is excluded from their diet. A pitfall, particularly for vegans (who will not consume any calories from dairy products), is to increase their consumption of bread, pasta and rice to make up their daily energy requirements. This will have detrimental effects on their insulin profiles and ultimately their weight.
In my experience most vegan and vegetarian eaters are much more aware of the quality of the food they are eating, and may be more inclined to prepare their own food. In addition, they may be more likely to avoid processed foods and fast foods. If they can avoid taking in too much sugar or refined carbohydrate (wheat), their set-point and therefore their weight will fall.
THIRTEEN
The Fat of the Land
Life Events, Hormones, Geography and Your Weight
Many of my patients (the ones who have not been obese from childhood) will describe a particular time in their lives when they started to gain weight. Prior to this, they had not even had to think about weight regulation – it just came naturally. Then something happened, some change in their lives that resulted in a period of runaway weight gain. The life events leading to weight gain commonly include:
Leaving home
Going to college
Getting married
Doing night shifts
Starting a new job
Moving to a different country.
Once they notice the extra weight they have put on, they try and do something about it. They take the advice of their doctor or dietician and go on a low-calorie diet (they might even buy the current ‘miracle diet’ book). Eventually (after transient weight loss) their set-point rises even further. This is when their troubles really start. Maybe after another ten or twenty years of repeated dieting and hiking their set-point further and further upwards they will develop leptin resistance (as described in chapter 5), leading to full-blown, uncontrollable obesity. This is the well-trodden path to the bariatric clinic that many of my patients have taken.
We know from chapters 3 and 12 why diets lead to a higher weight set-point: we are telling our bodies to prepare for future famines. But why do the other life events that my patients describe also lead to a rise in their set-points?
Let’s look at these common life events and see what has changed in the environment to cause a sudden shift in the weight set-point and weight gain. Once we understand what triggers those set-point rises, we will be able to take a step further in our quest to control it.
New Horizons
First we’ll look at leaving home and going to university. Why would a bigger ‘fuel tank’ be needed in these circumstances? Imagine young adults throughout history leaving the family tribe/home to venture off into the unknown – into the wilderness, where obtaining food might be less certain. It would be perfectly natural for the body to want a bigger fuel tank in this time of uncertainty. The elevation in the weight set-point in this case is probably brought about by the stress hormone cortisol. The same stress hormones are produced today by adolescents when they leave the family home to venture into the unfamiliar world of university.1 Cortisol, when given as a drug to treat inflammatory conditions, has the side effect of producing a voracious appetite and food-seeking behaviour (it can also drive you slightly manic as well – which would explain the behaviour of many fresher students). And an increased appetite leads to weight gain. Higher cortisol levels therefore lead to an elevated weight set-point, which explains the 12lb (5.5kg) weight gain often seen in first-year students.2
Stress ➞ higher cortisol ➞ HIGHER WEIGHT SET-POINT
I Pronounce You … Hungry
What about marriage? Why should this cause significant weight gain in both women and men during the first two years, in comparison to those who don’t marry?3 Is this due to stress as well?
Although relationships and marriage can bring their fair share of stress, the significant weight gain after marriage is not down to this. In fact, studies have shown that happily married couples have significantly less of the stress hormone cortisol than single people.4
However, marriage is often a precursor to starting a family, and newly married couples are more likely to have a baby in the first few years after their marriage than couples who are cohabiting. So for many couples, whether they know it consciously, or sense it subconsciously, marriage is the signal to start preparing the family nest. In this day and age a couple will make practical and financial plans. They may choose to live in a home that has spare capacity in case a baby arrives, and they will have financial reserves for this possibility – many couples put off their wedding until these practicalities are in place. They will also have sorted out home and life insurance to protect them against untoward events.
However, we have not always had the luxury of guaranteed shelter and food supplies – these are modern luxuries, and changes that our genes don’t understand. Throughout most of human history our nomadic ancestors would have had only one insurance policy available to them – their body’s ‘insurance’ against famine. From an evolutionary perspective, it would make sense if the weight set-point of both the man and the woman were raised when a new baby was imminent. Both parents might need more energy reserves in the event of a pregnancy. In biological terms, this is so that the woman can carry the pregnancy safely through, even in times of food shortage, and the man has the ability to protect and feed his new family.
For women, the extra energy reserves – in the form of fat – would insure a future pregnancy against food shortage. The extra weight would also improve her fertility. From a male perspective, having a female partner carrying your baby can also pose some new challenges, ones that are common to most mammals, particularly chimpanzees and other primates like us. Having to spend time securing your territory, and possibly deterring other males from your mate, could potentially mean periods without food while your guard duties are carried out. The only sensible insurance against this would be a pre-emptive weight gain – a larger ‘fuel tank’ might be needed to protect and provide for your new family. The mechanisms that cause the weight set-point to increase are unclear; however, we do know that after marriage men’s testosterone levels decrease and women’s oestrogen levels increase.5 A man’s lower testosterone helps family stability, but also leads to weight gain; and a woman’s higher oestrogen increases fertility, but also signals an increase in fat storage, particularly in the hips and breasts.6
After marriage, as the respective weight set-points of the couple increase (in preparation for a family), this drives their behaviour
and prompts increased appetite, food-seeking and hoarding as well as producing a slower metabolism to assist the weight gain. The explanation that weight gain after marriage is because couples are ‘happy’ and have ‘let go’ is probably not true: they are biologically programmed to gain weight.fn1
Marriage ➞ lower testosterone (males) ➞ HIGHER WEIGHT SET-POINT
Marriage ➞ higher oestrogen (females) ➞ HIGHER WEIGHT SET-POINT
Night Nurses
When I was a junior doctor I spent quite a lot of time on the ward at night. I have many fond memories of the quietness of the hospital at 3 a.m. – chatting and laughing with the friendly night nurses. One of the things I remember about the nurses that chose to do night work was their size. On average, they seemed to be about 2 stone (14kg) heavier than the nurses that worked the day shift. As a junior I assumed that maybe they had made the decision for a quieter life as a night nurse because they were overweight or obese. It was only when I started to speak to obese patients in my clinics that I realized the night-shift work was actually causing the weight gain.
Why We Eat (Too Much) Page 25