Why weight loss isn't as simple as a smaller piece of cake
Anyone who has ever tried to lose weight knows it's no piece of cake. But thanks to metabolic adaption, it's not a smaller piece of cake either.
Losing weight is a piece of cake.
Correction: losing weight is a smaller piece of cake because weight management is a question of counting Calories in and Calories out.
At least, that's what we're told.
If you want to lose weight, consume fewer Calories. This will create an energy deficit, and the greater that deficit, the more weight you will lose. Everyone and his dog knows this much.
The rule of thumb is that for every 3,500 Calories you remove from your diet, you will lose a pound in weight (a pound is equal to 453g). Cut 7,000 Calories and you should lose two pounds.
I’ll let Scotland’s national health information service, NHS Inform, explain why.
“One pound of fat contains 3,500 Calories so cutting your Calorie intake by 500 Calories per day on average, should see you lose one pound per week. While it might not seem like much, if you ate an extra 100 Calories per day, by the end of the year you could gain 11lbs.”
If you follow this advice and cut 500 Calories a day from your diet, you should lose one pound of weight a week. Over the course of a year, that adds up to a whopping 52lb (23.6kg). That’s almost four stone in old money.
52lb is a lot of weight to lose in a year, and we wouldn’t want you wasting away.
What about setting your sights a little lower, losing say a stone (6.35kg) in a year?
That’s easy. Remove the equivalent of a can of full sugar Coke from your daily diet, and a year later you’ll be 14lb lighter!
Who would miss a measly 139 Calories a day?
Losing weight really is a smaller piece of cake.
Or one less can of Coke.
Job done!
You’ve just been demobbed, a slither of your former self!
But don’t let me hold you back when you’re champing at the bit to take this fight to the enemy.
You're not reading this to be given a prescription of one less fizzy drink a day.
Most weight-loss diets advocate eating only 1,500 Calories a day and some go as low as 800 Calories. The much publicised Fast800 Diet requires you to eat 800 Calories a day for 12 weeks.
Men are said to need 2,500 Calories a day to maintain weight, so if you are overweight you are probably eating more than that. For argument’s sake, let’s say you currently munch your way through 3,000 Calories a day. Plenty of men do that and then some.
By cutting down from 3,000 to 1,500 Calories, you’ll be eating 1,500 fewer Calories a day.
That works out at 547,500 fewer Calories over the course of a year.
That’s right, half a million fewer Calories!
Congratulations, soldier!
You’ve just lost 156 pounds!
If you weighed a heavyweight 17 stone (108kg) at the start of the year you now weigh less than six stone (37kg) and are in a hospital bed being read the last rites!
The first casualty of war is the truth.
Hold on a minute.
Laid up in hospital with a priest by your bedside?
That can’t be right.
At ease, soldier. You can put the rosary beads back in the drawer because if you reduce your Calorie intake by 500 Calories a day, you will not lose a pound every week, and you will not lose 52lb in a year. And if you eat 1,500 fewer Calories a day for a year, you definitely won’t lose 156lb.
This is because the 3,500 Calorie rule does not hold true.
It doesn’t work for weight gain or weight loss.
Despite its near universal use by health organisations, there’s not a single scientific study that supports it either. Not one.
It is based on nothing more than the fact that a pound of fat contains 3,500 Calories. The assumption then is that a 3,500 Calorie shortfall in your diet will be made good by burning a pound of fat from your body’s fat stores. If correct, this would indeed result in you losing a pound in weight, but that’s not what happens. If you’ve ever attempted to lose weight, you’ll know that’s not what happens.
Maybe that’s because weight loss isn’t as simple as counting Calories in and out.
Maybe it’s not as simple as eating a smaller piece of cake either.
If I Only Had A Brain
Here’s something we can all agree on. Being overweight is the product of an energy imbalance. If you consume more Calories than you use, you will put on weight. Do this for long enough and you will become overweight. Keep going down this road and you may well end up obese.
It seems common sense then that to lose weight, we just need to eat less. Oh, and maybe move more for good measure. That’s exactly what we’re told to do if we want to lose weight. Eat less, move more.
But if losing weight was really that easy, we would all look like Gerard Butler in the film, 300.
Seriously, we would all look like Spartan warriors. As it is, we are more likely to land the role of Eglon, the fattest man in The Bible, not King Leonidas.
According to the 3,500 Calorie rule, the fat should melt away when we cut Calories, but what happens is nothing of the sort.
At first, you may experience rapid weight loss, but this is largely because of water loss, not fat loss. How that squares with the 3,500 Calorie rule I’m not sure because there are no Calories in water. Further weight loss will include not just fat, but lean body mass and perhaps even bone mass. Even your vital organs will shrink in size and contribute to weight lost.
The 3,500 Calorie rule accounts for none of this. It assumes all weight loss is fat.
Over subsequent weeks, and despite your best efforts, weight loss will slow. If you are still cutting Calories after a few months, chances are your weight will have plateaued or even started to increase.
Again, nothing about that in the 3,500 Calorie rule.
If you want to continue to lose weight, you will need to eat even less and move even more, but the time comes when you and your body have simply had enough of this deprivation. Saying no to a biscuit and walking up a flight of stairs to lose weight is one thing, practising starvation while doing Insanity workout classes quite another.
This is when your weight loss journey will grind to a halt. You’ll start eating more again and your weight will creep back up. Before you know it, you are back to where you started. You may even end up weighing more than you did originally.
So what’s really going on?
Let me break it to you gently.
You’re not the Scarecrow from the Land of Oz.
If you were a scarecrow, weight management would come down to nothing more than counting Calories in and counting Calories out, and the 3,500 Calorie rule would hold true.
You, however, have the one thing our man of straw does not, and it’s not dress sense.
You, my friend, have a brain.
The brain is the ultimate command-and-control centre. It’s what American theoretical physicist, Michio Kaku, describes as “the most complicated object in the known universe”.
Much of the brain's genius is dedicated to ensuring an adequate supply of nutrition and energy, but your brain is also the product of some four billion years of evolution, and therein lies a problem.
We are living through a period of evolutionary mismatch, one that pits the human brain against an alien environment. Our brains and our bodies evolved to survive and thrive in very different times and under very different conditions. The land of plenty we inhabit today has existed for much of my lifetime, and maybe yours too, but no longer. Compared to four billion years, or even the 350,000 years homo sapiens have walked this Earth, we’re talking a blink of an eye.
The daily lives of generation upon generation of our ancestors were dominated by the constant struggle to put food on the proverbial table. Little wonder then that the brain continues to value food and drink so highly, even at a time when both are available in embarrassing abundance. There were no 24-hour supermarkets, no American-style fridges, no fast-food restaurants, and no multi-pack chocolate bars in the Stone Age, during Roman times, the Middle Ages, in 1800, or even when my Mum was growing up in Glasgow’s East End.
When you diet, you are deliberately making food scarce, something that runs contrary to your very being. Your brain isn’t going to let you do that without a fight. It doesn’t know if it will be days, weeks, months even, before food is once again plentiful. Giving up valuable energy reserves in such circumstances would be a dereliction of duty. And so your brain doesn’t just meekly hand over body fat. Instead, the most complicated object in the known universe battens down the hatches.
This battening down is known in the trade as metabolic adaption, and it is metabolic adaption that blows the 3,500 Calorie rule right out of the water.
Metabolic adaption - commencing phys-ops
When you deprive your body of its usual supply of Calories, your brain acts to defend what it sees as valuable energy reserves by orchestrating a campaign of metabolic adaption. It’s akin to what the military calls psych-ops, psychological operations, but in the body’s case, phys-ops, or physiological operations, might be more appropriate.
Phys-ops involve physiological changes that obstruct or prevent weight loss and encourage weight regain. To picture how phys-ops might work, imagine that a tank of water represents your daily energy needs. Reducing the amount of water poured in will lead to a water shortage, but not if you introduce a hose pipe ban and less water is used. The hose pipe ban represents an example of metabolic adaption. And if you are successful at saving water in other ways too, you may well end up with more water than you need rather than a less.
Similarly, following metabolic adaption, you might cut Calories and end up with more surplus energy than you would have had if you hadn't cut Calories in the first place. You don't need to be a rocket scientists to know what that will do for your weight-loss efforts.
Thanks to metabolic adaption, getting your body to give up its fat reserves in the face of Calorie restriction can be like taking candy from an 800-pound gorilla.
Energy levels are an obvious target. The less you feel like doing, the fewer Calories you’ll use. Start cutting those Calories and you might not feel like climbing Kilimanjaro today. If you drag yourself to the gym, expect a half-hearted workout. Even poor Fido won’t get that long walk.
None of this happens by accident.
Your brain is working to make you less active.
Some of the energy-saving tricks employed are so subtle that you won’t even notice them. You might fidget less, for example, or slouch more (good posture requires more Calories).
But it’s surprising how little energy we use doing things anyway. Less than 30% of the Calories we consume on a daily basis are used to fuel physical activity, unless we are very active. Even strenuous exercise requires surprisingly few Calories. The energy needed to run a half marathon can be found in a Big Mac served with large fries and a large Coke. Which incidentally begs the question; if you’re not planning to run a half-marathon anytime soon, do you really need that “extra value” meal deal?
Most of the energy you use during a typical day goes towards maintaining bodily function and sustaining life. Even when you’re not climbing Kilimanjaro or walking Fido, or even sitting reading this book, your body does a million and one other things. Your heart beats, your brain computes, your lungs expand and contract, your nose hairs grow. All of this stuff requires energy, and this “necessary for life” energy requirement is what we call the basal metabolic rate (BMR).
For your body to function at this basal or resting level requires little more than a Calorie a minute, but with 1,440 minutes in a day those Calories add up. If you live a sedentary lifestyle, your BMR can account for as much as 80% of your total daily energy use. This being the case, your brain’s best shot at preserving energy and thwarting weight loss is to lower your BMR. No surprise then that doing exactly that is a key component of metabolic adaption.
One way your body achieves a fall in BMR is by increasing the efficiency of energy metabolism.
Before energy found in food and drink can fuel your body, it is broken down to form adenosine triphosphate (ATP). ATP provides the energy for virtually everything that happens in your body at cellular level.
When you diet, your body can up its game and create more units of ATP from each available Calorie of energy. This means you require fewer Calories to do the same things.
This ability to extract more ATP from each Calorie also benefits from a multiplier effect thanks to your body’s incredible ability to recycle energy. Your body recycles and reuses each unit of ATP 500 to 750 times a day. So although you consume say 2,500 Calories a day, your body is able to work with that and generate the equivalent of your body weight in ATP energy.
If your body couldn’t do this you would need to consume the equivalent of up to two years’ worth of Calories every single day! I said earlier that the energy required to run a half marathon can be found in a Big Mac meal. That’s only true because of the body’s recycling of energy: you’d be looking at eating 500 or more such meals otherwise.
And this brings us to the flip side of the ATP energy-recycling coin. For every Calorie removed from your diet, your body loses the ability to produce not only a certain amount of ATP, but multiples of ATP that recycling would have produced. Cutting 100 Calories doesn’t seem like much, but not eating that slice of bread means ultimately depriving your body of the equivalent of 20 loaves once ATP recycling is factored in.
The actual figures are more nuanced, and the physiology a lot more complicated. The impact of Calorie restriction will not be as big as the gulf between 20 loaves of bread and a single slice, but it will be many times greater than might be imagined. Your body will definitely know it is taking a hit, that’s for sure. Start cutting 500 Calories a day, as many diet plans advocate, and no wonder your brain does all it can to push back.
Your brain doesn’t stop at reducing energy expenditure either. No, sir. It will also do everything it can to make you eat more to replace any fat it is forced to give up.
Key to this aspect of metabolic adaption is an increased appetite. Although we often use them synonymously, hunger and appetite aren’t the same thing. Hunger is a physical sensation brought on by the need for food. Appetite is the desire to eat food. Professor John Blundell of the University of Leeds is one of the leading authorities on appetite control and he defines appetite more precisely as “a biologically driven behaviour expressed in a socio-cultural environment”. That’s because appetite can be brought on by hunger, but also by a wide range of social and environmental cues. For example, a television commercial might whet your appetite for junk food even when you are not experiencing hunger.
In determining appetite levels, your brain also responds to changing levels of hormones such as ghrelin, the hunger hormone, and leptin, the satiety or fullness hormone. More about the impact of these and other hormones on our bodies later, but you will no doubt have heard that weight control is largely a matter of willpower. I’m a big fan of positive thinking and the power of the mind, but you cannot will hormone levels to rise or fall, no matter how hard you try.
Metabolic adaption guarantees weight loss is not as simple as taking a smaller slice of cake. If we want to win this war, we're going to have to be a lot smarter than that.
Article last updated: 30th January 2021
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