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Yo-yo dieting

Studies on populations generally find that people who eat breakfast are thinner than people who skip it.¹ Yet those self-same studies generally also find that people who eat breakfast consume more calories over the course of the day than do skippers. How can we reconcile these data?

Well, one of the reasons people skip breakfast is that they’re dieters. And who diets? Large people. So an Australian survey of 699 13-year-olds, 12 per cent of whom skipped breakfast, found that girls who believe themselves to be fat will go on weight-loss diets, and they will do so in part by skipping breakfast.²

The girls in that Australian study may, of course, have had false body images, and they may not have been large, but a study on female college students in North Carolina found that 48 per cent of the obese ones had skipped breakfast, as opposed to only 40 per cent of the overweight ones and just 27 per cent of the normally weighted ones.³ So large people do indeed skip breakfast.

That particular North Carolina study covered only 166 subjects, so it missed being statistically significant (p<0.09 in the jargon), but multiple surveys have confirmed that skipping breakfast is a common reaction to overweight and obesity.⁴ Consequently, large people will diet and will lose weight but – and here comes a key point – dieters generally fail to keep down their weight, and in so-called yo-yo dieting they tend to revert to being large.⁵ So as people cycle between:

 being large and so losing weight by skipping breakfast

 being slim and so eating breakfast again

we have found one resolution to the breakfast/body weight paradox. I.e. when people are large they skip breakfast and eat less (so largeness is associated with skipping breakfast) but when people have slimmed down they eat breakfast and other meals again and, unfortunately, put the weight back on (so slimness is associated with eating breakfast). But it’s not the eating of breakfast that determines weight, it’s weight that determines the eating of breakfast. I.e., it’s not:

eat breakfast → consume more calories → paradoxically be slim

or

skip breakfast → consume fewer calories → paradoxically be large

rather it’s:

be slim → can afford to eat breakfast

or

be large → respond by skipping breakfast

Why do dieters return to their previous weight?

Just as Mark Twain is reported to have said that quitting smoking was easy, he’d done it a thousand times, so dieters find it equally easy to lose weight, they’ve done it a thousand times. But then they put it back on again, and repeated studies have confirmed that 80–90 per cent of dieters revert to their previous weight.⁶ At least five reasons have been proffered for this yo-yo dieting: namely (i) pleasure, (ii) the replacement of muscle by fat, (iii) resetting the basal metabolic and exercise rates, (iv) hormones and (v) genes.

Pleasure: Conventional dieting is rarely fun, and the temptation to start eating again at the end of a weight-loss diet is strong, so people who skipped breakfast when dieting will, on breaking their diet, eat it again (thus, incidentally, creating the paradox of large people skipping breakfast and slim ones eating it).

The replacement of muscle by fat: Dieters do not lose only fat: many researchers report that dieters, on losing weight, lose muscle mass as well. But on recovering their weight, former dieters put back more fat than muscle. And because fat consumes less energy than muscle, the former dieter – if they want to maintain a fixed weight – needs to eat less food than before, which they will generally fail to do.

The first study to report this so-called ‘preferential restocking of fat tissue on refeeding’ was the famous Minnesota starvation study that the now notorious (see later) Ancel Keys performed over 1944/45. Concerned by the mass starvations of the Second World War, and believing (rightly) that they needed to be better understood, Keys recruited thirty-six conscientious objectors (male, lean, aged 22–33) with his celebrated advert, ‘Will you starve that they be better fed?’ He then indeed starved – and re-fed – his volunteers, and in his classic 1950 book The Biology of Starvation he reported the preferential restocking of fat tissue on re-feeding. And though not all researchers, on repeating Keys’s experiment, find the preferential restocking,⁷ most do:⁸ for once Keys told it like it probably is. Only if dieters consume a reasonable amount of protein – and take exercise – will they help sustain muscle mass.⁹ My wife tells me, by the way, that this knowledge is widely known by personal trainers.

Resetting the metabolic and exercise rates: The Biggest Loser is an American reality television show where people compete to lose weight. Some people achieve massive weight loss (Danny Cahill, who is now 46, from Season 8, lost 239 pounds – 17 stones or 108 kg – in seven months) but, as the New York Times ran on its front page for 2 May 2016, these contestants then hit the problem of ‘adaptive thermogenesis’ (from the Greek therme, ‘heat’, and gignesthai, ‘to be born’), which is a posh way of saying that human bodies will vary the amount of energy they use.

To be anthropomorphic, our bodies do not want to lose weight: our bodies are programmed by evolution to see starvation as a terrible threat, so a body that has experienced significant weight loss will, in a response that is sometimes known as the Survival of the Fattest, save energy by decreasing its metabolic rate. And that decrease may apparently be permanent. Nor are we talking small differences: in the words of an influential study: ‘A formerly obese individual will require about 300–400 fewer calories per day to maintain the same body weight and physical activity level as a never-obese individual of the same body weight and composition.’¹⁰

The Biggest Loser research study from the National Institutes of Health, on which the New York Times based its story, found that the figure was higher, around 600 calories a day.¹¹ This number of calories is almost the size of a meal, and someone who’s dieted will have to skip it permanently if they’re to maintain the same weight as someone who’s never dieted. Danny Cahill, for example, failed to do so, and he’s now 104 pounds (7 stones 6 pounds, or 47 kg) heavier than he was seven years earlier.

Although some studies fail to find adaptive thermogenesis in dieters (which in the interests of balance I note here)¹², the majority do, and so we see how adaptive thermogenesis fights dieters. And, actually, it does so not only by slowing down their rate of metabolism but also by reducing the intensity of a phenomenon that is not widely recognised, namely casual exercise.

Physical activity can be monitored by portable meters or ‘accelerometers’ (the precursors of activity trackers such as Fitbits and Jawbones) and it transpires that dieters and post-dieters engage in less casual activity than their non-dieted peers: so dieters and post-dieters might take a lift rather than climb the stairs, or they might fidget less or drive short distances where once they would have walked.¹³ Dieters and post-dieters seem, therefore, to lose the spontaneous impulse they once had to climb stairs or stretch their legs.

Adaptive thermogenesis thus offers another explanation for the paradox of breakfast skippers consuming few calories while being large: breakfast skippers will often be yo-yo dieters who (1) because of adaptive thermogenesis will burn relatively few calories, yet who (2) because of the yo-yo will be large. But it wasn’t the breakfast skipping that enlarged these people, it was the yo-yo dieting-induced adaptive thermogenesis.

Hormones: Our hormones also don’t want us to lose weight; a research group from Melbourne, Australia, found that overweight or obese subjects, on losing a significant amount of weight, demonstrate – even a year after the diet has stopped – higher levels of hormones such as ghrelin (which increases hunger) and lower levels of hormones such as leptin (which decreases hunger).¹⁴

Genes: Is our weight determined by our genes or our environment? Professor Tim Spector, the twin expert from King’s College London, has found that: ‘on average identical adult twins are less than 1 kg different in weight.’¹⁵

Genetics, in short, play a huge role (about two-thirds of the influence) in setting a person’s weight,^fn1 and only about a third of the influence is due to the environment.¹⁶ If we diet, therefore, in Professor Spector’s words: ‘Our bodies simply seem to adapt to the reduced calorie intake and do what they are programmed by evolution to do … This is why most diets fail.’¹⁷

Worryingly, weight-loss dieting might even induce weight gain. In 2012 a research group from Finland reported on identical twins where one of the twins had deliberately lost at least 5 kg (11 pounds, ¾ stone) on at least one occasion but where the other twin had never gone on a diet. And the dieters had eventually ended up, on average, 0.4 kg (1 pound) heavier than the non-dieters.¹⁸

Conclusion: A group from Switzerland, on reviewing the field, has concluded that slim people should never diet: they risk eventually putting on weight. Only large people should diet: only for them might it lead to weight loss.¹⁹

Dieting being unexpectedly problematic, we need to identify a strategy – a lifestyle – that allows people to lose weight and to keep it off. As we shall see, skipping breakfast will help achieve that.