Kitabı oku: «The Way We Eat Now», sayfa 6

2: Mismatch

‘Sometimes we need to step backwards.’ Thus begins one of the many voices on the internet suggesting that our eating would be healthier and happier if only we could travel in time and eat a bit more like our great-grandmothers. This particular article – from the Institute for the Psychology of Eating – goes on to recommend ‘ancestral eating’ as the solution to many of the health problems of modern times.

What, you may ask, is ancestral eating? Apparently, it means sticking as closely as possible to the diet of your great-grandparents, wherever they happen to have lived. If your ancestors came from Greece, ancestral eating might entail full-fat yoghurt, wild greens, grass-fed meat and olive oil; if your family came from Japan, it might include fish, seaweed, fermented vegetables and ‘heirloom’ grains.¹

Nostalgia for the tastes of our childhood has always been a powerful emotion. In our modern food environment, many of us invoke the wisdom of our grandparents as a way out of the craziness and ill health of modern diets. The inspiration for much of this way of thinking comes from the food writer Michael Pollan, who memorably advised that a good rule of thumb for healthy eating was ‘Don’t eat anything your great-grandmother wouldn’t recognise as food.’

The urge to turn back the clock on modern diets is understandable. So many aspects of our diets have worsened in recent decades. In all regions and in all countries, diets rich in coarse grains, legumes and other vegetables are disappearing as a mainstream way of eating and, as we saw in Chapter 1, there has been a great loss of biodiversity. It’s true that almost anyone in the modern world would be nutritionally better off eating more olive oil, more vegetables, more fish, more lentils, more wholegrains.²

Yet there are significant problems with thinking that the solution to poor diets is to go backwards. For one thing, our great-grandmothers often suffered terribly for the food they made, as they toiled to grind enough grain to keep their families alive. Until recently, it was common for women in much of the world to suffer from severe arthritis in their upper bodies, caused by the hours they put in at the grindstone, and rolling dough for such staples as chapattis and tortillas.

Moreover, not all great-grandmothers were eating an ideal diet. Many of our recent ancestors, as we’ve seen, were eating an extremely monotonous diet of grains and teetering on the brink of hunger. True, your great-grandmother wouldn’t recognise ‘sports drinks’ or popcorn fried chicken or any of the myriad other new highly processed foods, but she also might not recognise many of the wholesome new foods that contribute to health: raw kale salad and overnight oats and pumpkin seeds. Some great-grandmothers, moreover, were eating an early twentieth-century version of junk food. In 1910 a public health campaigner in New York City watched school children buying hotdogs dyed with violently pink food colouring and frosted cupcakes. It’s simply not true that our great-grandmothers would only recognise meat that was organic or grass-fed.

There is yet another difficulty with calling on the wisdom of our great-grandparents to save us from the worst excesses of modern food. This way of thinking ignores the fact that we are already living and eating with one foot in the past. Many of our most profound problems with eating stem from our inability fully to adapt to the new realities of the nutrition transition. In many ways, we already are eating according to the wisdom of our great-grandmothers, whose physiology and attitudes to eating were forged by the constant threat of scarcity.

What we eat may have radically changed in our lifetimes, but our food culture has not changed quickly enough to keep pace. We may, sadly, have forgotten the recipes of our great-grandmothers. Most of us have lost their home-spun knowledge of how to bottle fruits for the winter, not to mention their brilliance with a carving knife. But what we have not forgotten is their excitement at a laden table. We are living in a world of perpetual feast but with genes, minds and culture that are still formed by the memory of a scarce food supply. This is part of what it means to live through the vertiginous changes of stage four. We haven’t yet developed the new strategies for living that would enable us to navigate our way through this forest of seeming plenty to a way of eating that gives us both health and pleasure.

Think about some of the eating strategies that would have made sense in an era of scarce food. For one thing, you would value energy-dense foods such as meat and sugar very highly and gorge on them when they came your way – just as many of us still do. You would leave a clean plate and when food was accessible, you would grab it while you could.³

Development experts speak of ‘mismatch’ in explaining the clashes between the new food reality and the persistence of a human biology and culture adapted to earlier times. Instead of looking backwards to some imagined past which we can never reclaim, we need to look forwards and have yet another change of taste.

Our food system is currently full of mismatches. Some of these mismatches are cultural, as we fail to adapt to the new realities of eating in an age of abundance. Our food culture remains far too misty-eyed about sugary foods, for example. We haven’t adjusted emotionally to the fact that sugar is no longer a rare and special celebration food, worthy of devotion. Nor have we yet modified our attitudes towards those who are overweight and obese, to reflect the fact that these people are now in the majority.

Perhaps the most tragic mismatches are biological, as bodies formed for an environment of scarcity have not adapted to cope with the strange and bountiful new world we now find ourselves eating in.

The thin-fat baby

It was 1971 and Dr Chittaranjan Yajnik was a young medical student training at Sassoon General Hospital, Pune, a big city in the west of India. Yajnik was given the task of measuring the body mass index (BMI) of diabetic patients. This should have been a routine job, little more than number crunching. The main challenge was that Yajnik could not afford a calculator, so he laboriously wrote down the patients’ weight in pounds and height in feet in a log table and used his paper notes to calculate in his head the BMI in kilograms per metre squared.⁴

After taking measurements for the first ten patients, Yajnik noticed something was not right about his numbers. His medical textbooks had taught him that type 2 diabetes was a disease mostly suffered by the old and the obese. But the first ten diabetic patients that Yajnik measured in the hospital at Pune were all young and thin, with low BMIs. If his measurements were correct, then the textbook must be wrong, or at least incomplete, in its definition of type 2 diabetes as an offshoot of old age and obesity. Yajnik tried to raise the problem with his medical supervisor but was told that this was no time to be challenging medical orthodoxy – he should just focus on passing his exams.⁵

Yajnik could not put the puzzle of diabetes in India out of his mind. After some years studying Western diabetes in Oxford, England, he returned to Pune as a fully qualified medical researcher, by which point diabetes was on the rise in his home country. In the early 1990s, Yajnik began a study following mothers and their babies in six rural villages near Pune – the Pune Maternal Nutrition Study. The data he started to gather confirmed his hunch that diabetes in India had a very different face from the supposedly classical type 2 diabetes in the textbooks. Yajnik took detailed birth measurements of more than six hundred Indian babies and compared them with a cohort of white Caucasian babies born in Southampton in the UK. Compared to the UK babies, the Indian babies were smaller and lighter. Yet when Yajnik used calipers to measure the thickness of the babies’ skinfolds, he found that the small Pune babies were actually fatter than the Southampton babies – they were surprisingly ‘adipose’, especially around the centre of the body. Yajnik coined the phrase ‘the thin-fat Indian baby’ to describe this phenomenon. Even at birth, these Indian babies had higher rates of pre-diabetes hormones in their bodies than their British equivalents. The babies may have looked thin but their body composition was actually fat.⁶

We speak of conditions such as heart disease and type 2 diabetes as ‘non-communicable diseases’ or NCDs. You can’t catch an NCD from another person in the way that you would catch a common cold by standing next to someone who is sneezing. But what Yajnik discovered is that babies can actually ‘catch’ a predisposition towards diabetes from their mother in the womb, via the diet she eats. The babies of mothers who were undernourished during pregnancy had ‘fat-preserving tendencies’ – passed on as a survival mechanism.⁷

It used to be believed that India’s diabetes epidemic was mainly due to ‘thrifty’ genes, endowed over many generations on populations that suffered from patchy and inadequate food supplies. Thanks to decades of malnourishment, these populations were poorly adapted to eat a rich modern diet. Yajnik’s breakthrough was to show that the time frame of maladaptation was much shorter. He speaks not of a thrifty gene but a ‘thrifty phenotype’: the interaction of genes with the environment over a single generation. Depending on the environment in which it develops, a given gene may give rise to different phenotypes. The ‘thin-fat’ baby represents a mismatch of biological environments. These babies grew inside their malnourished mothers with phenotypes for hunger but – thanks to the huge changes in India’s food supply between the 1970s and the 1990s – found themselves eating an unexpectedly plentiful diet.⁸

When Yajnik first observed the ‘thin-fat’ baby in the 1990s, this was a radically new way of thinking about the interaction of nutrition and health. It took six years for Yajnik to have his first paper on the subject accepted for publication because the mainstream medical establishment was so sceptical of this idea ‘coming from an obscure Indian in an obscure place’, as he puts it. The idea of the ‘thin-fat’ baby only started to gain acceptance when Yajnik published a paper in 2004 revealing that he was a ‘thin-fat’ Indian himself.⁹

This 2004 paper – which he called the ‘The Y-Y paradox’ – included a now-famous photograph of Yajnik side by side with his friend and colleague John Yudkin, a British scientist: two slim middle-aged men in white shirts. The paper explained that Yajnik and Yudkin had near-identical body mass index readings of 22 kg/m². A BMI of anything between 18.5 and 24.9 is considered healthy in the UK: not underweight and not overweight. Yajnik and Yudkin were both well within this healthy range. But X-ray imagery showed that Yajnik – the thin-fat Indian – had more than twice the body fat percentage of his friend. Yudkin’s body fat was 9.1 per cent whereas Yajnik’s, despite his slim appearance, was 21.2 per cent. Further research has confirmed that the adult Indian population in general has lower muscle mass and higher body fat than white Caucasians or African Americans.¹⁰

The story of the thin-fat babies of India is the story of the nutrition transition written on human bodies. Thanks to the new science of epigenetics, we now know that a pregnant woman’s body sends signals to her unborn child about the kind of food environment he or she will be born into. An underweight pregnant woman who eats a scarce diet is signalling to her child that food will always be scarce, which triggers a series of changes in the baby’s body, some hormonal and some physiological. For example, Yajnik found that a lack of vitamin B12 in the mother’s diet resulted in babies who were more likely to be insulin resistant.

Thin-fat babies are graphic evidence of a society in a state of dietary flux, with a shift from starvation to abundance in a generation. These Indian babies were born to mothers who lived and ate not so long ago, but the circumstances of their lives feel like another universe. There was seldom enough food, especially fats and protein, and people had to walk many miles just to get fresh water. When these women became pregnant, their babies’ bodies were metabolically programmed before birth – with their ample deposits of abdominal fat – to survive in circumstances that were harsh and lean. But the babies grew up eating in a very different and more affluent environment: a world of improved buses and electricity and labour-saving farm machinery, of cheap cooking oil and rising incomes. Millions of people in Indian cities – a new and rising middle class – have scooters where once they had only bicycles or feet. Diabetes is the worm in the apple of this new Indian prosperity.

The problems of babies born into a rapidly changing food environment are compounded by the way they are fed during the early years of life. The memory of scarcity still informs the strategies mothers use to feed babies, not just in India but everywhere in the developing world. Many of the thin-fat babies will have been fattened up in their first two years by emergency food aid. In the old India, the most urgent nutrition problem was outright hunger and overfeeding a child seemed to be the last thing anyone should worry about. This hungry India still exists to a shocking extent, with 38 per cent of all children under five so short of food that it will impair their future development, according to the Global Nutrition Report. If the alternative is to starve, rapid weight gain in the first two years of a child’s life can be a miracle. But it’s now known that this rapid growth in children who were previously malnourished may have unintended long-term consequences. Rapid growth is a risk factor for obesity and elevated blood pressure in later childhood and diabetes in adulthood. There is gathering evidence that high intake of protein and vegetable oils during the early years of feeding may result in a higher risk of obesity later in life.¹¹

Given India’s vast population, it is perhaps not so surprising that the country currently has more patients with type 2 diabetes than any other in the world. The more startling fact is that people with diabetes form such a high percentage of that population. Already, in large cities such as Chennai, around two-thirds of the adult population is either diabetic or pre-diabetic.¹²

What can be done to correct the nutritional mismatch suffered by the thin-fat babies? Those working with malnourished babies in developing countries have started to talk of ‘optimal’ nutrition: the kind of childhood diet that will provide all the essential micronutrients and promote growth while minimising excess weight gain. Yajnik and his colleagues are currently working on a project giving a cohort of adolescent girls vitamin supplements which should, in theory, mean that in pregnancy their bodies will send the message to their unborn children that a world of plenty awaits them. The aim of the project is to get the bodies of the mothers to communicate more accurately with their unborn children about what food is like in modern India and thus to reduce the risk to future generations of developing NCDs. Only time will tell if these hopes come to fruition. The epigenetic messages in our bodies cannot be rewritten straight away.

Spare a thought for the grown-up thin-fat babies of the 1980s and 1990s, many of whom are now diabetics living in modern India. Through no fault of their own, these people are stuck while young with a disease they will spend a lifetime trying to manage. Living with type 2 diabetes means living on a diet that is directly at odds with the prevailing food supply. In food markets awash in lavish amounts of refined carbohydrates, they must teach themselves to be sparing with sugar and white rice. They must try to limit their calorie intake in a world that offers them ever-larger portions.

The dilemmas faced by the thin-fat Indian are an extreme version of the problems facing millions of others in the modern world. We are all affected to some degree by a series of biological clashes between the basic instincts of our bodies and the environments in which we live, and taken together, these clashes seem almost designed to make us fat. Every human baby has an inbuilt preference for sweetness, which didn’t matter too much in the days when sugar was a luxury, but which becomes a problem in a world of cheap sweeteners. We also have a natural inclination to conserve energy, which served us well as physically active hunter-gatherers and farmers but doesn’t pan out so well in cities full of cars. Many of the human instincts that evolved to help us survive have now become a liability. Yet another example is the fact that, in human biology, hunger and thirst are two separate mechanisms, which means we can drink almost any amount of sugary drinks without deriving much satisfaction from them.

The thirst conundrum

Where do you draw the line between a drink and a snack? These days, it can be hard to tell. If you eat a serving of chocolate ice cream, it counts as dessert and gives you approximately 200 calories. But if you take the same chocolate ice cream in the form of a large milkshake, the serving size may yield as much as 1,000 calories. Yet because it’s only a drink, you might have a burger and fries alongside.

It doesn’t make sense to talk about changes to eating habits without bringing in the revolution in what we drink. Perhaps no single change to our diet has contributed more to unthinking excess energy intake than liquids, both soft and alcoholic. We have reached a state where many people, adults and children, can no longer recognise a simple thirst for water, because they have become so accustomed to liquids tasting of something else.

By 2010, the average American consumed 450 calories a day from drinks, which was more than twice as many as in 1965: the equivalent of a whole meal in fluid form. Whether it’s a morning cappuccino or an evening craft beer, a green juice after a workout or an anytime bottle of Coke, the choice of calorific beverages available to us has become immense and varied. Around the world, there are bubble teas and agua frescas; cordials and energy drinks; and then there are all the new-fangled ‘craft sodas’ infused with green tea or hibiscus that pretend to be healthy, even though they probably contain nearly as much sugar as a Sprite. Many modern beverages are better thought of as food than drinks, judging by the number of calories they contain. Yet for reasons both cultural and biological, we don’t categorise most liquids as food. To our bodies, this endless stream of drinks registers as little more satisfying than water.¹³

Picture a typical day for an average Westerner, and start counting the drinks. It’s a lot. It surprised me to learn that more than 5 per cent of Americans now start the day with a sweetened fizzy drink, but then again, cola for breakfast is a logical enough choice if you work early shifts and don’t have access to a kitchen. A more universal morning drink is coffee, which is often more milk than coffee. Maybe there’s an orange juice on the side. (After decades of growth, however, our appetite for orange juice is finally waning, hit by growing consumer awareness that it is little more than sugar. From 2010 to 2015, the amount of Tropicana fruit juices consumed in the US dropped 12 per cent.) By mid-morning, survey data suggests that 10 per cent of Americans are ready for another coffee or soda. Personally, I am in awe of anyone who waits that long. I am so addicted to coffee, particularly when working, that I am often thinking about my second cup before I have finished the first (which is one of the reasons why I try to take my coffee black as the default. Try).¹⁴

And so our days continue, punctuated by sips of sugar-water and caffeine of one kind and another, with or without the addition of milk and various syrups, until the cocktail hour arrives, time for more soft drinks or alcohol. We sometimes imagine that the Mad Men generation of the 1950s were much bigger drinkers than the average person today. But except for a small affluent minority, Americans consumed vastly less alcohol in the 1950s than today – total alcohol intake increased fourfold from 1965 to 2002 in the US.¹⁵

This is a global story. A rise in beverage consumption is one of the key elements in the nutrition transition, wherever it has happened. In 2014, a market report on soft drinks wrote of Latin America as ‘the global bright spot for soft drinks brand owners and bottlers’.¹⁶ Young people in the emerging economies of Mexico and Argentina drink more of these drinks every year, as incomes increase. In China, people who lived their whole lives drinking nothing but unsweetened tea and water now have access to beer and fizzy drinks and a whole smorgasbord of Starbucks flavoured coffees.

It’s a sign that times are good when you can afford to quench your thirst with liquids other than water. The drinks industry – both soft and alcoholic – has conditioned us to believe that whatever the occasion, it will be improved with a drink in our hand. Studying? An energy drink will help you concentrate. Out with friends? You need a beverage to help you relax. By 2004 the average American was consuming 135 gallons of beverages a year other than water – around one and a half litres a day.¹⁷

Wine glasses in England from 1700 to 2017: a sevenfold increase in size (based on an article by Theresa Marteau and colleagues in the British Medical Journal 2017).

It would be easy to paint all this modern beverage consumption as a novel kind of gluttony which those wise great-grandmothers of ours would never have indulged in. But in middle-income countries such as Mexico where much of the water supply is unsafe, buying soft drinks can be a move of self-preservation. Bottled drinks do not contain the bacteria of unclean water and are less likely to make you and your children sick. What’s more, a fizzy drink can look like the frugal choice. Given the option between paying a similar amount for a bottle of water or a bottle of cola, the cola can appear to be better value, because it offers flavouring and energy along with the liquid.

But our biology is not well adapted for this switch to high-calorie beverages. When we talk about what’s wrong with modern drinks, we discuss the problems with sugar, but we don’t talk so much about our own hunger and fullness. It seems that our genes have not evolved to be satisfied by drinking clear liquids, even when those liquids contain as much energy as a three-course lunch. This is the liquid conundrum. A person might easily drink two large glasses of Chardonnay before dinner, and then go ahead and eat a substantial meal as if nothing had happened (or maybe this is just me). Another person might have half a litre of Mountain Dew and feel no less hungry for a foot-long sandwich. With certain exceptions, our bodies simply do not register the calories from liquids in the same way that we do with solid food. This is one of the starkest mismatches between human biology and our current patterns of consumption.

Before the first experiments with honey-wines around 11,000 years ago, the only drinks available to humans were water and breast milk. For most of our evolution as a species, drinks and food were thus two entirely separate things, except for babies. There were survival benefits to keeping the mechanism of thirst separate from the mechanism of hunger. If hunter-gatherers had become full from drinking water, they wouldn’t have felt the need or desire to go out and search for food, and they would have died.¹⁸

Numerous studies have shown that most people do not compensate for the energy they drink by eating less. When you drink water, it rapidly enters your intestine, quenching your thirst but doing little to dent your hunger. The same is true even when the water is laced with sugar. It’s as if our bodies simply don’t register the calories in the same way when they arrive from a glass, a cup or a can. Clear fluids such as sports drinks, fruit juices, cola and sweetened iced teas seem to be particularly bad at killing hunger, but milk-based drinks such as lattes and chocolate milk are also surprisingly unfilling for most people, despite the nutrients they contain. Scientific studies show that people have a weak satiety response to clear drinks regardless of how many calories they are laden with – meaning that they don’t fill us up as much as the equivalent calories taken as food. And so we end up consuming a lot more energy from drinks than we intended or even knew.¹⁹

As of the year 2000, sugary drinks were the single largest source of energy in American diets. Westerners have been drinking sugar-sweetened tea and coffee for a few centuries, but never before have ‘caloric beverages’ taken up so large a proportion of the average diet. In the past, the largest source of energy in human diets would have been a staple food that actually filled a person up, such as bread. It’s a sign of how disconnected we are from our own hungers that we have reached the point when so many people receive most of their energy from something that gives our stomachs so little satisfaction.

The relationship between liquids and hunger is still not fully understood. One biological explanation for our lack of fullness after a drink is that the normal hormones – peptides – that are triggered in our gut when we eat food are not triggered when we drink sugary or alcoholic drinks. The role of these hormones is to signal to our brains that we are full. When we have a large sugary drink, there is faulty communication between our gut and our brain and somehow we don’t get the message that we have just ingested hundreds of calories.

We need a way to think about liquid-fullness as well as food-fullness. I’ve found it helpful to start telling myself that anything other than water is a snack not a drink: to be savoured, not gulped down. A cappuccino can taste amazingly creamy and delicious when you tell yourself it’s food. Whether this kind of mindful drinking would work when you have just ingested three beers and are wondering about a fourth on a Friday night is debatable, however.²⁰

There are exceptions to the rule that liquids don’t fill us up. After all, breast milk is both food and drink to a baby. Some liquids – soup being the prime example – are actually even more filling for most people than solid food. The thickness or viscosity of a liquid seems to be important for whether it is filling or not. The more viscous a liquid is, the more it suppresses hunger.²¹ Our beliefs about different liquids may also affect how much satisfaction they bring us. Soup has a long-standing reputation as satisfying – something that nourishes us and feeds us, body and soul. A cold, fizzy drink, by contrast, has no such nourishing connotations.

The rise of highly marketed calorie-filled drinks is a big part of why our energy balance – calories in and calories out – is so out of sync. The average BMI of the US population has been increasing for over 250 years but it only took a sudden sharp turn upwards in the mid to late 1970s. This was the same moment when the daily energy gained from beverages suddenly increased – from 2.8 per cent of all energy to 7 per cent for the average person. Correlation is not causation, but the timing supports an association between rising beverage intake and rising obesity. The correlation between a sudden growth in consumption of caloric drinks and increasing BMI maps onto the whole population, across all ages and ethnic groups.²²

Mainstream opinion will – charmingly – tell a person that if he or she is fat, the reason must be a lack of willpower. But the example of calorie-laden drinks shows once again that obesity cannot simply be attributed to individual laziness or greed. Around forty years ago, companies began marketing a completely new set of drinks to American and European consumers. Another couple of decades on and these novel liquids were travelling the world and becoming ever larger. In 2015, Starbucks marketed a cinnamon-roll-flavoured frappuccino that contained twenty teaspoons of sugar (102 grams) in a single serving. In some ways, the surprise is not that two-thirds of the population in the UK and US are overweight or obese; but that one-third of the population are not.²³

Yet we live in a culture that says that despite all this sugar being pumped into our drinks, we are not allowed to be fat. This is one of the cruellest aspects of our current food culture. There is a huge mismatch between the availability of foods and drinks and the way we talk about the people who consume the most everyday and easily available items.