A deficiency, as a driver of obesity, would fit in with the weight set-point theory that we discussed in chapter 1. To recap, the weight set-point theory says that the subconscious brain (the hypothalamus) is responsible for calculating the weight that is best for us. It uses data from our genes and environment to calculate our own individual weight set-point. A change in the environment, i.e. a deficiency of an essential food, could turn the set-point upwards. Once the weight set-point is elevated (above the actual weight of the person), the subconscious brain drives the weight towards the new set-point by strong appetite signals (by giving you a voracious hunger) and a reduction in metabolism (making you tired and listless). Next thing you know … you are hungry all the time, can’t stop eating and your weight is on the rise.
This would be a completely left-field way of looking at obesity. The voracious hunger, coupled with listlessness, would no longer be seen as the cause of the disease, but as a symptom of it – just as the tiredness of scurvy sufferers was recognized as a symptom of the condition, and not the cause of it, once vitamin C had been discovered. History would be repeating itself. But more importantly we would have an effective strategy to treat obesity.
What’s Missing?
Let’s go on a detective hunt for our deficiency. We need to answer three questions:
When did obesity rates start to rise?
What happened to our food at this time?
What was removed or replaced?
The first question is easy to answer: obesity rates started to increase dramatically in the mid-1980s. What happened to our food at this time? Government healthy-eating guidelines happened.
In 1977 the McGovern Report, Dietary Goals for the United States (discussed in chapter 8), was released to a trusting public. The guidelines were produced in response to a dramatic rise in heart disease following the war. The diet–heart hypothesis, despite many scientists disagreeing with it, underpinned the dietary guidelines. Saturated fat was demonized as the root cause of the heart disease epidemic (and still hasn’t recovered, see Appendix 1). So the obesity epidemic coincided with a big change in the advice to the population on what to eat. If our deficiency theory holds true, then some essential element of the diet must have been removed or replaced at this time.
Figure 9.1 US obesity rates, 1960–2008 Source: C. L. Ogden and M. D. Carroll (2008). Prevalence of Overweight, Obesity, and Extreme Obesity among Adults: United States, Trends 1960–1962 through 2007–2008. National Health and Nutrition Examination Survey (NHANES), June. National Center for Health Statistics.
‘Healthy’ Vegetable Oils Take Over
One of the most striking changes in eating behaviour that occurred was the replacement of saturated fats (found in butter and lard) with vegetable oils such as cotton seed, safflower, rapeseed (canola) and sunflower oil. Vegetable oils had also been hailed as protective of the heart: they had been shown to decrease the level of blood cholesterol, and this, it was assumed (if you went along with the diet–heart hypothesis), would decrease the risk of heart disease. Vegetable oil consumption skyrocketed from 15lb/year in 1970 to over 60lb/year in 2009, a rise of 300 per cent (see Figure 9.2).
The ‘safer’ alternative to butter, a semi-solid mix of vegetable oils called margarine, remained popular. Flora, sponsors of the London Marathon, became the symbol of healthy man-made foods.
The change in the type of fats that were consumed had a downside, however. Even though the amount of saturated fat consumed continued to decline, the increased intake of vegetable oils, shortenings (a solid form of vegetable oil used for baking) and margarine actually led to a rise in the total amount of fat consumed: a rise of 63 per cent from 1970 to 2005.
Figure 9.2 US added fat intake per person, 1960–2009 Source: Data from the USDA Economic Research Service.
A Gift to the Wheat and Corn Farmers
The dietary goals document also recommended a second critical change: the increased consumption of grains, which were considered healthy for the heart. The rise in the amount of grains consumed suited the US Department of Agriculture, which had vast reserves of wheat and corn to sell. The Western public duly followed this advice, resulting in an increase in wheat flour consumption from 115lb to 150lb per person per year from 1980 to 2000. The guidelines had envisaged people consuming whole grains, but the vast majority of wheat consumed was highly refined, and therefore had a similar effect on people’s insulin levels as table sugar. Insulin levels, as we discuss more fully later in this book, also play an important role in determining our weight set-point.
The dietary guidelines did not stimulate a public interest in home cooking; on the contrary, people were increasingly confused by what to eat, and as a result more and more processed food was sold – quite often with reassuring labels, such as ‘low cholesterol’ or ‘heart healthy’. Most of the dramatic rise in the consumption of both vegetable oils and refined grains was in the form of these processed foods. The cheap oil and grain commodities could be mixed with whatever other flavourings, preservatives and e-additives were required to make biscuits, crackers, cakes, soups and gravies etc.
Figure 9.3 Daily calories consumed by the average American, by food group, before the obesity crisis (c.1970) and after the peak of the crisis (c.2010) Source: Statistics from the USDA Economic Research Service, Pew Research Center, Washington DC, US.
Food Changes Just before the Obesity Epidemic
So, in summary, the changes in our diets just before the spike in obesity that started in the 1980s were:
Increased vegetable oil
Increased grains
Increased processed foods.
When you glance at the figure above, the major changes in our eating patterns become clear. Meats, eggs, dairy, fruit and vegetable consumption were all pretty similar. The rise in sugar consumption was small (30kcal). But consumption of grains rose by 170kcal/day and added fats from vegetable oils by a massive 240kcal/day.
What is Missing?
Our final question on the hunt for our deficiency – what was taken out of the food we consumed as a result of these changes? Did the dramatic rise in vegetable oil consumption, combined with food-processing techniques, somehow cause a micro-deficiency of a food essential for our health? Recent research into lipids (fats) suggests that this may indeed be the case, and that these changes may not only be contributing to obesity but also to other common Western diseases such as heart disease, autoimmune conditions and cancer. Our scientific understanding of the function of fats within our bodies lags far behind our understanding of vitamins. This fascinating new area of research is now trying to piece together the relationship between the type of fat consumed in our diets and the development of Western diseases, including obesity.
To help us understand the potential lipid (fat) deficiency that may be contributing to the obesity crisis, let’s take a refresher in fats and what they do within our bodies.
Apart from their energy-storing capacity, fats have many other vital functions. Our brains and nerves are predominantly made up of fats; in fact the brain consists of 50 per cent cholesterol, so fat is essential for normal nerve and brain function. Our hormones, which are powerful drivers of behaviour, are also made from fats. These include our sex hormones (oestrogen and testosterone) and stress hormones (cortisol). Our inflammatory processes, which coordinate the repair of tissues and fight against infections, are driven by messengers derived from fat. Finally, and probably most importantly, fat makes up the cell walls of every organism on Earth, and cell walls act as the final barrier to, and conduit from, the outside world to our very core, our DNA.
Into the Frying Pan
There are three different types of fats. Each fat molecule is made up of a chain of carbon atoms.
Each of the carbon-to-carbon bonds in the chain holds the precious energy contained within the fat. One end of the carbon chain is attracted to fat – this is called the omega end. The other end of the carbon chain is attracted to water – this is called the alpha e
nd. This configuration, the carbon chain having one fat-loving end and one water-loving end, is called a fatty acid: this is how fat exists within the body. Think of the fat molecule as a long dining table in a medieval banquet, with the king and the queen (with their different attractions) sitting at either end.
Figure 9.4 Composition of fat molecules
The number of ‘guests’ sitting at the dining table determines the type of fatty acid that it will become. In fatty acids, the ‘guests’ at the table are hydrogen atoms. If the dining table is full of ‘guests’, and there is no room for any more, then it is called a saturated fatty acid. These are quite rigid and unbending. They are also very stable and will stack on top of each other and easily make solid structures.
Saturated fats, because of this stability, are solid at room temperature. Examples of foods containing a lot of saturated fat are: butter, lard, cheese, palm oil, coconut oil and animal fats. When the dining table is full, apart from a single seat that is left free, the fat is called a monounsaturated fat (mono = one). This type of fat is slightly more flexible than the rigid chains of saturated fat. Because of this it is liquid at room temperature but will solidify when in the fridge. Examples of foods containing this type of fat are: olive, peanut and avocado oils.
When the dining table has several seats still available, the fat is called a polyunsaturated fatty acid. These are much more bendable and flexible than saturated or monounsaturated fats and are therefore liquid at room temperature and also in the fridge (think cooking oil).
The Special Fats
There are two special types of polyunsaturated fatty acids. These are called omega-3 and omega-6 fatty acids and are different to all other types of fat.
Figure 9.5 Composition of a saturated fatty acid
The other fats, the saturated or monounsaturated ones, can be made by us, within our own bodies. We are not reliant upon them in our diets. As we know, the saturated fat cholesterol is an essential component of our brains and our cell walls, and therefore essential to our health. If we don’t eat foods containing cholesterol (as some dieticians might advise) our bodies will take over and produce it from scratch within the liver.
The omega fats are unique: we are unable to make these fats ourselves. Just as for vitamins, we are reliant on eating foods that contain them. They are therefore known as essential fatty acids – because it is vital to our wellbeing that they are part of our diet.
Omega-3 and 6 may seem similar, but before we go any further I want to highlight some important differences in them so that you can understand how each of these fats affects your body.5 First, omega-3 has a much curlier and more flexible carbon tail and moves faster than omega-6, changing shape many times per second. It therefore makes any tissue that contains it much more flexible, faster and more adaptable. This is a very important trait of omega-3 within our bodies. Secondly, omega-3 gets oxidized much more quickly than omega-6. This means that when exposed to oxygen it will break down, or decompose, more easily. Think of what happens to food when it is left out and unattended: it goes brown and decomposes – this is oxidation. Fresh foods that go rancid quickly, if left out, tend to have high levels of omega-3 (e.g. fish).
So, we have identified these two types of fat that, like vitamins, are essential in our diet to maintain health. Could the changes to the types of fat we now consume – the changes brought about by the dietary guidelines of 1977 and coinciding with the start of the obesity crisis – have led to a deficiency of these essential fatty acids? Let’s examine where they are produced in nature.
Figure 9.6 Composition of omega-3 and omega-6 fatty acids
OMEGA-3 OMEGA-6
Carbon tail Curly, dynamic, fast-moving Slower and stiffer
Makes tissues More flexible, adaptable Less flexible, adaptable
Oxidation Easily decomposes More stable
Table 9.1 Characteristics of omega-3 and omega-6
The Sunshine Fat – Omega-3
As the sun shines on our rainforests, meadows and seas, a process essential to all life on Earth is taking place. Embedded within the cells of all green leaves, and within all plankton and algae floating on the sea, are structures called chloroplasts. Chloroplasts are the plant equivalent of our own cellular energy factories (our mitochondria). However, they can be considered the most important structures on Earth. They function to take the energy from sunlight and convert it into chemical energy. This energy is used to produce more and more complex fats, proteins and carbohydrates so that the plant or plankton can grow and survive. The precious energy that these structures produce forms the basis of the food supply to every other creature on Earth, from the cattle and fish eating them to larger predators – including us.
All the biological energy on Earth stems from chloroplasts. But they produce something else that is essential to us as well. Chloroplasts produce omega-3. And because the world has a lot of rainforests, vast meadows and grasslands and abundant algae floating on our oceans, omega-3 is the most common fat in the world. You would never have thought that a serving of spinach or lettuce contains a fat that is so abundant, and so essential to our health.
Omega-3 is passed through the food chain, so that any animal or fish that ingests green plant matter will therefore also contain omega-3 within its cells. Fish, which don’t have much food choice except plankton, therefore contain large amounts of omega-3. Any type of animal that grazes on grasses, such as sheep or cows, will also contain high levels of omega-3 in its body. A predator that eats the animal that ate the green leaves or grasses will integrate the omega-3 into its tissues as well. At the top of the food chain are human beings, and as long as we consume lots of omega-3-containing vegetables or the fish or cattle that have themselves fed on greens we will also have abundant omega-3 within our own bodies.
The Autumn Fat – Omega-6
Omega-6, the other essential fatty acid, is also made by plants, but it appears in their seeds and not in their green leaves. As with omega-3 it is passed through the food chain, so it will be abundant in animals that consume seeds – and in the animals that prey on the animals that consume the seeds.
So how did the changes in the type of foods that we were eating at the beginning of the obesity crisis affect the amount of these essential fatty acids in our diet?
The Verdict – Rapid Rise in Omega-6
To recap, the American dietary guidelines recommended decreasing the amount of saturated fat consumed and increasing the amount of grains in the diet. Much of the saturated fat was replaced by vegetable oils; in fact, overall the amount of fat consumed increased. The vegetable oils that replaced saturated fat are made from seeds and therefore contain abundant omega-6.
Soybean oil now accounts for 50 per cent of the vegetable oils consumed in the USA. They contain 54 per cent omega-6 fat by volume; that is 120kcal per tablespoon. This is now the most common oil that is added to processed foods.
The bar chart overleaf confirms the considerable quantities of omega-6 fats present in most vegetable oils compared to omega-3. The exceptions are cod liver oil (originating from plankton-eating fish) and butter, which has mostly natural traditional saturated fats and low levels of polyunsaturated fats.
The dietary advice to increase the amount of grains (seeds) eaten would also have increased the amount of omega-6 in our diets. What about processed foods? We know that processed foods contain lots of vegetable oils and refined grains like wheat, so again omega-6 will be plentiful. Far from causing a deficiency of this fat, the dietary guidelines led to an unprecedented increase in the level of omega-6 in our bodies. To those who still adhere to the diet–heart hypothesis, and remember the effect omega-6 has in decreasing the cholesterol level in the blood, this would seem like a helpful change to our diet. Let’s test it …
Figure 9.7 Omega-3 (light grey) and omega-6 (dark grey) and levels of common cooking oils and spreads. Units mg per tablespoon (14g) Source: Data courtesy of USDA National Nutrient Database for Standard Reference: Nutrition Data; https:
//nutritiondata.self.com.
A 2013 study, published in the esteemed British Medical Journal, looked at what would happen to our health if we replaced saturated fats with omega-6 fats. The rationale of the study was that populations living in the Western world have been encouraged to make this dietary change, even though it has not been robustly tested. The study compared two groups, each containing about 220 men who had recent heart problems. One group was to continue eating their normal diet containing saturated fats, and the other was to replace these fats with linoleic acid – safflower (a type of seed) oil and margarine (omega-6). The outcome? ‘Substituting dietary linoleic acid in place of saturated fats increased the rates of death from all causes, including heart disease.’6 Despite the clear conclusions of this study (and many similar ones), the dietary advice we receive remains the same. The NHS still advocates omega-6 vegetable oils in place of saturated fats. The diet–heart hypothesis remains entrenched at the centre of this advice, seemingly unmovable in the face of mounting evidence against it (see Appendix 1 on cholesterol at the end of the book for more detail).
Figure 9.8 Increasing levels of linoleic acid (omega-6) found in body fat in American citizens, 1961–2008 Source: S. Guyenet (2011), Seed oils and body fatness – A problematic revisit. Whole Health Source, 21 August.
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