‘Fat controllers’ tell our bodies when to eat and when to stop but the role of genes and hormones is far from simple.
It is a fair bet that, on the subject of food, former Australian Prime Minister Tony Abbott and the late great psychologist BF Skinner would have locked horns. With two thirds of Australian adults overweight or obese Abbott is on the record as saying, “No one is in charge of what goes into my mouth except me”. But Skinner was the principle architect of behaviourism, a view that downplays free will and stresses the environment as a cause of human action. Now governments grappling with soaring global obesity rates are lining up behind their chosen contender.
For libertarians like Abbot, obesity is strictly a “fork to mouth” disease, the buck stops with each of us, and the answer is education about diet and nutrition. Progressives, however, blame a world awash with cheap, calorie-dense foods whose precisely pitched flavours defy even staunch resistance. The liberal solution is regulation, including taxes on soft drinks, bans on junk food advertising, and an urban makeover friendlier to pedestrians and cyclists. But working out who holds the reins on what we eat is not just a policy issue. It is critical for the torrent of adults desperately trying to curb their own weight.
Camilla, a Melbourne-based businesswoman, attests to the daily personal toll of obesity. She chooses aisle seats on planes so her bulk only encroaches on one other passenger and when meeting clients in restaurants arrives early to scan for chairs without constricting arms. She even kept her composure when a hotel doorman greeted her with raised eyebrows and an imperious, “I don’t think you’re staying here are you?”
Camilla grew up mixed-race in 1980’s South Africa where apartheid meant, as a dark-skinned six year old, she was exiled to the street when her fair Irish mother had to shop in the “whites only” grocery store. And the tensions didn’t end at her door step. “I lived in a very volatile family so I turned to food to comfort me,” she says. But despite all the potential culprits for overeating in her early life, Camilla is loath to point the finger elsewhere: “I’ve always felt that it was my own responsibility. But it’s not a choice to be overweight. Because if I could choose this is not how I would want to be.”
The high failure rate of diets and the burgeoning view that bariatric surgery, which makes the stomach smaller and often bypasses it, is one of the few effective weight loss treatments, raise serious questions about whether “willpower” has any role in weight control. These questions have been an abiding concern for Professor Alexandra Logue from the City University of New York.
As a fifteen year old Logue swapped summer vacation for a science course that left an indelible mark. She trained rats to push marbles into a hole using Skinner’s operant conditioning, where behaviour is shaped by reward and punishment. It wasn’t long before she was a Harvard Psychology graduate student with an office next to the celebrated Skinner himself. Nearly forty years later Logue’s book The Psychology of Eating and Drinking is in its fourth edition, she is a card-carrying behaviourist and, while noting the importance of genes, she believes much eating behaviour is, quite simply, learned.
“What you do is a function of your physiological status, what is around you, and the interaction of that,” Logue’s voice crackles over a faltering Skype connection. She doesn’t believe in a “homunculus”, or little Wizard of Oz pulling levers in the brain. When it comes to food we dance, rather, to the beat of an environment increasingly engineered by food purveyors. And for Logue there is one foodstuff that carries particular cachet.
The honey roasted peanut manages a feat that nature on its own never could. It combines three elements which, in isolation, are merely alluring but in combination become irresistible: sugar, salt, and fat. This chimerical food is a behaviour “reinforcer” that prompts us to reach for its tantalising reward again and again. But, as Logue notes, how much reward we get from food is critically dependent on our inner workings, and it is in this realm that we are seeing seismic shifts.
The body is generally good at homeostasis, keeping variations in things like temperature to a minimum and, for much of human history, weight has been no exception. We chomp through about a million calories a year and our weight varies less than five kilograms over a decade. And a set point for weight makes evolutionary sense; too thin and we risk starvation, too fat and our sluggish bulk runs the gauntlet of predation. Yet adult obesity rates have nearly tripled in developed countries, from 25% in 1980 to over 68% in 2012. So what might be loosening the firm grip of energy homeostasis?
The humble rat offers the beginning of an answer. Given a choice lab rats turn their noses up at standard rations of soybean, corn and fish meal in favour of the “cafeteria” diet that features stars of the sugar, salt and fat brigade like Fruit Loops, peanut butter cookies and Lay’s chips. And they duly stack on the pounds. But this is no whimsical preference: the critters will endure electric shocks and extreme cold to get their junk food fix, even when the bland healthy stuff is available by the bucket load.
For Homo sapiens the world has become one big cafeteria. In the last fifty years the proportion of total US food spending on fast food rose from 2% to 18% and soft drink consumption increased 3.5 fold. Distasteful, yes, but the comparison with our murine friends starts to look chillingly accurate. And anyone wondering why could do worse than study a hormone that has been hogging the limelight since it was discovered a little over twenty years ago.
The “satiety hormone” leptin is made in fat tissue and regulates weight by keeping the brain updated on the state of fat stores. If victuals are scarce and fat reserves dwindle leptin drops, a change sensed by the brain’s all purpose thermostat, the hypothalamus. The upshot is you feel hungry and move around less in a two-pronged strategy to conserve energy. In times of plenty when fat stores rise, so too does leptin, which makes you feel full and stops overeating. But, somewhat mysteriously, leptin can work very quickly, way before any changes in fat mass.
To understand why, I asked Professor Michael Schwartz, Director of the Diabetes and Obesity Centre of Excellence at the University of Washington. Schwartz explains that leptin production alters according to the metabolic state of the fat cell. Just skipping lunch can shift fat cells into catabolic mode, leptin secretion plummets, and you get hungry. No longer just a static energy depot, fat is shaping up as a dynamic endocrine organ to rival the pancreas or the thyroid gland.
But the outward march of girths suggests leptin isn’t quite the failsafe fat controller. When obesity takes hold leptin goes up, stays up, and there is a gradual resistance to its effects. The brain starts to react as if there is no leptin at all, thinks you’re starving, and goes into hungry/ don’t move mode. Suffice to say that hunger, like the need for sleep, sex or breathing, is a biological drive that can be resisted for only so long. But what might be messing up the “I’m full” signal that leptin is usually so good at delivering?
Schwartz tells me one of the prime suspects in leptin resistance is dietary fat. Within days of gorging on lard, beef tallow and coconut oil rats mobilise inflammatory cells in the hypothalamus. Says Schwarz, “These cells are hallmarks of the response to neuron injury. Consuming the diet is actually doing something to damage the neurons that are supposed to protect against weight gain”. But fat has an accomplice. Fructose, ubiquitous in the flavour enhancer high fructose corn syrup, causes leptin resistance in rats. And so the evidence is mounting that the cardinal ingredients of the Western world’s new favourite diet are actually making us hungrier.
If you have any doubts that leptin holds titanic sway over the urge to eat consider what happens when you can’t make any at all. This is the miserable lot of children with a single mutation affecting the ob gene. They become morbidly obese, something that is almost miraculously reversed with leptin replacement. Indeed, variants in genes coding for leptin and a host of other proteins involved in energy homeostasis are major contributors to obesity worldwide, accounting for up to 70% of the variation in body mass index.
At first glance, this might seem an open and shut case for genetic determinism, the idea that our fates are inextricably those of our genes. But it is worth remembering that even a complete absence of leptin does not cause obesity on its own. You need the food too. And both our genes and physiology are doing a complex tango with a world that pushes our food buttons with unprecedented sophistication.
Bärbel Knäuper, Associate Professor in Psychology at McGill University in Montreal, tells me: “The food industry is trying their best to condition our behaviours. They have it easy because they are doing this for high fat and sugar foods, which are super-rewarding. It is so much harder to hook people on healthy foods because the brain does not react favourably to them.”
Knäuper explains that classical conditioning – think Pavlov’s dogs – plays a big part. Let’s say you’re partial to a packet of crisps while watching television. The crisps are a reward you learn to associate with TV. Pretty soon you’ll expect the reward whenever you pick up the remote and, before you know it, you’re heading for the pantry. Food marketers have seized on this to create the brave new world of snacking, where any time can be the right time to eat and any activity a cue. Something to think about the next time you head for that latte after dropping the kids at school.
The power of food cues came to striking prominence in a study by Paul Rozin and colleagues published in Psychological Science nearly two decades ago. They fed a standard lunch to two men with amnesia so severe they could remember nothing beyond the previous minute. The men duly ate it. Remembering nothing of that first meal, they promptly ate a second meal of the same size twenty minutes later. This went on until a fourth sitting when one of the men complained his, “stomach was a little tight”. The lesson is clear. When it comes to regulating food intake feelings of fullness are soundly trumped by the simple cue, “It’s lunch time”.
For Alain, a Melbourne health academic, the potency of food cues holds little surprise. A gay man in his fifties, Alain recounts a boyhood plagued by a sense of “otherness” and isolation that turned him first to books then, fatefully, to Coca Cola and chocolate. Seven years ago, after myriad attempts to lose weight, he had lap band surgery and lost fifty kilograms. Twenty kilograms gradually crept back, at least in part because Alain, as he puts it with self-deprecating wit, is an “adept cheat”. He would flush food through his shrunken stomach so he could eat more. Why? “Because I had a mental picture of what a normal meal should look like”.
Psychologists call the desire to eat what we think is the right amount “unit bias”. And that unit is often the size of a bowl. Brian Wansink and colleagues showed this emphatically in a 2005 study where they served people soup in a bowl that would sneakily self-fill. Those people ate 73% more than a control group with normal bowls, yet felt no fuller. Wansink concluded that people, “use their eyes to count calories and not their stomachs”.
To make matters worse, food cues actually drive changes in the endocrine system. Simply thinking about mouth-watering dishes can have similar effects to eating them, hiking up insulin, dropping blood sugar and perpetuating hunger. So if your belly aches when you pass that Ben and Jerry’s billboard, maybe cut yourself some slack.
Have we really so little control over what we eat? Is willpower just a comforting myth? Free will has been on the mind of Neil Levy, Professor of Philosophy at Macquarie University and the University of Oxford, for much of his professional life. Levy, like Camilla raised in apartheid South Africa, grew up sharing his parents’ strident opposition to racism.
Mindful his view was through a white lens, and driven by academic curiosity, Levy submitted years later to a test of unconscious racial attitudes. Like many who abhor racism he did surprisingly badly. Levy tells me, “I became aware that I had attitudes that were hard to eradicate. That motivated my worrying about the extent to which enculturation excuses, or on the other hand, whether it’s reasonable to expect us to be able to assess and reject our enculturation.”
I see parallels in Levy’s experience and our pervasive food culture that often seems dissonant with free choice. But Levy is well aware of a threat to free will that runs deeper than enculturated attitudes: a surprising number of neuroscientists think free will is simply an illusion. And many of their doubts converge on a 1983 experiment by American physiologist Benjamin Libet.
At first glance Libet’s experiment looks childishly simple. He asked people to just flick their wrist whenever they felt like it, then note down the time when they first felt the urge to do it. To help tell the time there was a clock with a fast moving hand that swept around 60 numbers in three seconds. Meanwhile Libet recorded their brain activity with electrodes on the scalp.
As expected, people noticed the urge to move their wrist slightly before they did move it. But something odd was also showing up. The electrodes were picking up brain activity before people even felt the conscious urge to move. In fact, nearly half a second before, which is no snippet in brain time.
Libet used this brain signal, the so-called “readiness potential”, to suggest something that strikes at the very heart of humanism and the enlightenment tradition; wrist movements were being initiated unconsciously. The conscious urge was just an “epiphenomenon”, an after the fact rationalisation that sprung up automatically to explain something we’re loath to accept; we might not be the authors of our own actions.
While Libet’s findings have generated great controversy they were just common sense to many neuroscientists, few of whom accept the “dualist” idea of consciousness set out by French philosopher Rene Descartes nearly four centuries ago. Descartes proposed a conscious “self” that dispatches orders to a willing brain whose activity then brings about actions. His
“dualism” refers to the distinction between the spectral “self” and the physical brain.
But most neuroscientists demur, arguing consciousness must be a product, not a cause of brain activity. For what could consciousness be if it were causing the brain to splutter and spark but, as the British philosopher Gilbert Ryle put it, a “ghost in the machine”? Neuroscientists, evidently, don’t believe in ghosts. Libet’s results made sense because, if the conscious urge is a product of brain activity, then the urge must come after the activity. What role then, if any, do neuroscientists see for human will in the execution of actions?
Patrick Haggard, Professor of Neuroscience at University College London, set out his views in a 2008 article in Nature Reviews Neuroscience. To start, recall that many movements are reflexes. If someone taps your biceps with a tendon hammer your arm will move up automatically but you can also execute the same movement as “an act of will”.
Haggard explains that many actions sit somewhere on the spectrum between reflex and voluntary. You can drive along, manipulating gears, brake and accelerator to obey traffic lights and avoid road hazards, all the while engaged in deep conversation with a passenger. This happens effortlessly and, almost, without conscious intention.
Haggard doesn’t think decision making is necessarily linear, from agent to intention to action. Rather it may be more like a loop from the environment to an unconsciously processing brain to action. This fits with the idea, made prominent by Nobel laureate Daniel Kahneman in his book Thinking Fast and Slow, that we have a “fast” unconscious system that continually extracts data about the world. On this view the “will” might be like an autopilot adjusting course as new information comes quietly to it.
In 2009 Jennifer Harris at Yale University ran a study that showed how food choices might be silently relegated to the unconscious. Her team split school children into two groups to watch a TV program. One group saw the program with ads for games while a second group saw ads for waffles, fruit roll ups and potato chips that depicted people having a good time.
Students had a bowl of cheese crackers within reach and were told they could snack. Kids who watched the food ads ate 45% more crackers than their fellows. This is an example of “priming”; the ads triggered both the concept and the reward of food which “primed” – made more psychologically accessible – the related behaviour “eating”. A similar finding in adults is that food made visible and available on a desk, for example, is consumed in greater amounts than when placed on a more distant shelf.
All this might look like the bitter end for free will and food, but there could be a phoenix in the ashes. Levy is what is termed a “compatibilist” about free will. He accepts the possibility of “determinism”, the view that every effect, including all human action, is preceded by a cause and that, as a result, if we knew every fact and physical law we could predict human behaviour. Some philosophers think determinism spells doom for free will because it means humans are nothing more than effete cogs in a clockwork universe. But Levy thinks that determinism, if it were true, is compatible with having free will. This is because even when we act without intention, we can still act according to reason.
Let’s say you’re waiting at a pedestrian crossing, headphones on, listening intently to a lecture on free will. The green man lights up and you make your way across. Deep in concentration you don’t consciously register the green signal or a decision to walk. But on Levy’s view you are still a free-willing agent if, somewhere along the line, the rational you has endorsed green men as a reason to cross roads. Your decision to cross may be automatic, but it is executed as part of a considered game plan and is hardly random. Could the power of reasoning also salvage free will about food?
New research gives hope that it may, suggesting we can deploy rationality to change later unconscious responses to food cues. Take the example of “delay discounting”, an everyday fact of psychology that makes us downplay uncertain future rewards in favour of smaller rewards that are certain now. Obese people seem to have delay discounting amped up, attaching only a miserly value to the long term benefits of weight loss compared to the sure-fire reward of food right now.
A recent study by Tinuke Daniel and colleagues published in Psychological Science shows how this might be countered. They had overweight adults vividly imagine a happy future event, like a romance or a party, while weighing up whether to take $10 now or $100 down the track. Visualising a rosy future made the delayed reward more attractive. But the clincher came when they had people graze for 15 minutes on an all you can eat smorgasbord while listening to an audio of their own descriptions of that happy future. They ate nearly 20% fewer calories than a control group.
How it works is not entirely clear but Knäuper tells me, “Interventions that make an abstract future reward more concrete and bring it closer to the present have been shown to work”. As visualisation brings the distant reward of health closer it may trigger positive feelings sufficient to compete with the more palpable reward of food within arm’s reach. This fits with findings that successful weight loss is often preceded by a triggering event, like an abnormal ECG, getting diabetes, or not being able to fit into a wedding dress. These, too, may work by heightening the salience of the delayed rewards of weight loss.
But Knäuper counsels caution: “The problem is to get people to apply these interventions all the time. How do we get people to vividly imagine future health rewards faced with strawberry shortcake at a party? For really changing people’s eating behaviours, one has to change their habits”. And pre-emptive reasoning might be key here too.
Knäuper argues that just saying “No” to the shortcake is much harder than planning to do something else altogether. She coaches her weight loss trial participants with “if-then” strategies like, “If I’m offered a sweet then I’ll opt for the salad instead”. This technique, developed by New York University’s Peter Gollwitzer, forges habits by associating the food cue with an alternative healthier response that carries its own reward.
But Logue has an alternative to supersizing agency: why not manipulate the very cues that drive automatic decisions? “Pre-commitment devices” include taking less money to the supermarket, only shopping at places with healthy food and thinning out the stocks of goodies around the house. But Logue is leery of pronouncing cure: “Even the best behavioural techniques won’t have a lasting effect without certain things. And a big one is exercise. But of course you can use pre-commitment to help you with exercise”.
Amid the hope, Michael Schwartz is circumspect and his message sobering: “It’s really very complicated. It’s very difficult to generate a cohesive, integrated explanation that unifies all the different perspectives that are out there”. If anything is clear it is that human will is sandwiched between a yielding internal milieu and a world of eating cues that often just bypass consciousness. Meanwhile, both citizens and governments might heed Skinner’s closing, albeit gendered and enigmatically circular words on the human predicament in Beyond Freedom and Dignity: “[Man] is indeed controlled by the environment, but we must remember it is an environment largely of his own making”.
Abbott is on the record as saying, “No one is in charge of what goes into my mouth except me” – Four Corners “Generation O”. 2005. At: https://www.abc.net.au/4corners/fat-chance/5811768
The honey roasted peanut manages a feat that nature on its own never could – Logue AW. Hunger, satiety, and food preferences: effects of the brain and the body on the self-control of eating. In: Dube L, Bechara A, Dagher A, Drewnowski A, LeBel J, James P, et al., editors. Obesity prevention: the role of the brain and society on individual behavior. San Diego: Academic Press; 2010. p. 115-23.
We chomp through about a million calories a year and our weight varies less than five kilograms over a decade – The Biologic Basis of Obesity: A Lecture by Jeffrey Friedman, MD PhD https://www.youtube.com/watch?v=kNotqromxjQ
a set point for weight makes evolutionary sense – Friedman JM. Obesity: Causes and control of excess body fat. Nature. 2009;459(7245):340-2. Epub 2009/05/22.
Yet adult obesity rates have nearly tripled in developed countries, from 25% in 1980 to over 68% in 2012 – Ogden CL, Carroll MD, Flegal KM. Prevalence of obesity in the United States. JAMA. 2014;312(2):189-90.
lab rats turn their noses up at standard rations …the critters will endure electric shocks and extreme cold to get their junk food fix – Guyenet SJ, Schwartz MW. Clinical review: Regulation of food intake, energy balance, and body fat mass: implications for the pathogenesis and treatment of obesity. The Journal of clinical endocrinology and metabolism. 2012;97(3):745-55.
the proportion of total US food spending on fast food rose from 2% to 18% and soft drink consumption increased 3.5 fold – Guyenet and Schwartz
But, somewhat mysteriously, leptin can work very quickly, way before any changes in fat mass – Guyenet and Schwartz
Schwartz tells me one of the prime suspects in leptin resistance is dietary fat – Thaler JP, Yi CX, Schur EA, Guyenet SJ, Hwang BH, Dietrich MO, et al. Obesity is associated with hypothalamic injury in rodents and humans. The Journal of clinical investigation. 2012;122(1):153-62. Epub 2011/12/29.
fructose, ubiquitous in the flavour enhancer high fructose corn syrup, causes leptin resistance in rats – Shapiro A, Mu W, Roncal C, Cheng KY, Johnson RJ, Scarpace PJ. Fructose-induced leptin resistance exacerbates weight gain in response to subsequent high-fat feeding. American journal of physiology Regulatory, integrative and comparative physiology. 2008;295(5):R1370-5.
variants in genes coding for leptin and a host of other proteins involved in energy homeostasis are major contributors to obesity worldwide – Willyard C. Heritability: The family roots of obesity. Nature. 2014;508(7496):S58-60. Epub 2014/04/18.
Pretty soon you’ll expect the reward whenever you pick up the remote – Stich C, Johnson PJ, Knauper B. Resisting temptations: how food-related control abilities can be strengthened through implementation intentions. In: Dube L, Bechara A, Dagher A, Drewnowski A, LeBel J, James P, et al., editors. Obesity prevention: the role of the brain and society on individual behavior. San Diego: Academic Press; 2010. p. 343-52.
a study by Paul Rozin and colleagues published in Psychological Science nearly two decades ago – Rozin P, Dow S, Moscovitch M, Rajaram S. What causes humans to begin and end a meal? A role for memory for what has been eaten, as evidenced by a study of multiple meal eating in amnesic patients. Psychological Science. 1998;9(5):392-6.
Psychologists call the desire to eat what we think is the right amount the “unit bias” – Polivy J, Herman PC. Restrained eating in a world of plenty. In: Dube L, Bechara A, Dagher A, Drewnowski A, LeBel J, James P, et al., editors. Obesity prevention: the role of the brain and society on individual behavior. San Diego: Academic Press; 2010. p. 135-46.
Brian Wansink and colleagues showed this emphatically in a 2005 study – Wansink B, Painter JE, North J. Bottomless bowls: why visual cues of portion size may influence intake. Obesity research. 2005;13(1):93-100.
Simply thinking about mouth-watering dishes can have similar effects to eating them – Logue at p. 118
Levy submitted years later to a test of unconscious racial attitudes – see, for example, the Harvard Implicit Association Test at: https://implicit.harvard.edu/implicit/Study?tid=-1
And many of their doubts converge on a 1983 experiment by American physiologist Benjamin Libet – Libet B, Gleason CA, Wright EW, Pearl DK. Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act. Brain : a journal of neurology. 1983;106 (Pt 3):623-42.
Patrick Haggard…set out his views in a 2008 article in Nature Reviews Neuroscience –Haggard P. Human volition: towards a neuroscience of will. Nature reviews Neuroscience. 2008;9(12):934-46.
Jennifer Harris at Yale University ran a study that showed how food choices might be silently relegated to the unconscious – Harris JL, Bargh JA, Brownell KD. Priming effects of television food advertising on eating behavior. Health psychology : official journal of the Division of Health Psychology, American Psychological Association. 2009;28(4):404-13. Epub 2009/07/15.
A similar finding in adults is that food made visible and available on a desk, for example, is consumed in greater amounts – Painter JE, Wansink B, Hieggelke JB. How visibility and convenience influence candy consumption. Appetite. 2002;38(3):237-8. Epub 2002/06/20.
A recent study by Tinuke Daniel and colleagues published in Psychological Science shows how this might be countered – Daniel TO, Stanton CM, Epstein LH. The future is now: reducing impulsivity and energy intake using episodic future thinking. Psychological science. 2013;24(11):2339-42.
successful weight loss is preceded by a triggering event – Wing RR, Phelan S. Long-term weight loss maintenance. The American journal of clinical nutrition. 2005;82(1 Suppl):222S-5S.