Metabolism: it isn’t what you (probably) think it is. Strictly speaking, your metabolism is the sum of every chemical reaction in every one of your cells – the total energy you burn each day.
Suffice to say, it’s quite complex. But, when thinking about weight loss, your metabolism can be broken down into several key components. The most significant of these, which guzzles up around 60 per cent of your daily calories, is basal metabolism.
“Basal metabolic rate is the number of calories your body’s using on a minute-by-minute, hour-by-hour basis when at rest, simply to keep going,” says Dr Adam Collins, Associate Professor of Nutrition at the University of Surrey.
As he explains, basal metabolism is the energy expenditure of basic bodily functions – from pumping materials between cells to maintaining your circulation and vital organs. Your brain and liver alone account for half of your energy costs at rest.
Collins – who’s worked with people from all sectors of society, from sedentary types to elite athletes – knows the importance of metabolic health for quality of life, whether that’s ascending stairs or racing faster at the business end of a marathon. He also has a revelation for you: any weight-loss programme isn’t all about accelerating your essential processes.
“Some people think they’re obese because they have a slow metabolism,” he says. “But, unless you have an underactive thyroid, generally that’s not the case. Actually, the larger you are, the faster your resting metabolic rate is compared with that of a leaner individual – your body demands more calories just to keep going.”
In a clinical setting, it’s possible to calculate your exact resting metabolic rate – calorie requirements – using an astronaut-style helmet and analysis machine. When I tried it at Liverpool John Moores University, mine clocked in at around 1,900 calories per day. (I’m 1.89m/6ft 2in tall and 90kg/198lbs). That’s at the high end; for most people, it’s between 1,000 and 2,200 calories.
“It’s also worth noting that your metabolic rate will probably drop if you diet, exercise and lose weight,” says Collins. This is evident in elite athletes whose metabolism is so dialled in and efficient that their hearts barely beat and their lungs resemble bellows.
For them – being capable of, say, cycling over a high Alpine pass – sustaining a sedentary life is child’s play. One famous example from sporting circles is five-time Tour de France winner Miguel Induráin, whose resting heart rate was a mere 28bpm.
Though clearly important, your basal rate isn’t the entire jigsaw, but it is a piece of it. “Arguably more important is that we look at a person’s metabolism as containing three elements,” says Javier Gonzalez, Professor of Nutrition and Metabolism at the University of Bath.
“First, you have your resting [basal] metabolic rate. Then there’s the thermic effect of food – the energy required to digest and metabolise what we eat, typically about 10 per cent of our overall energy expenditure. Finally, you have physical activity. This is the component that we can manipulate significantly, by changing how much we move.”
In other words, improving your metabolic health doesn’t have to be a gruelling war on one front. Instead, there are several simple, science-backed lines of attack to increase your calorie expenditure. Here are the most effective…
1. Up your strength training
In general, the more muscular you are, the higher your resting metabolic rate. That’s why hitting the gym may yield greater metabolic dividends than swimming, cycling or running. “To a degree, all types of exercise will build muscle,” says Collins. “But clearly you’ll build greater muscle mass if you strength train.”
Lifting weights damages muscle, prompting it to repair and rebuild. Do this consistently and you’ll add muscle mass, which burns through calories during the workout and keeps them smouldering afterwards.
“This is known as the ‘afterburn effect’,” says Collins. “The more technical description is excess post- exercise oxygen consumption (EPOC). As you recover from high-intensity exercise, you go from creating energy anaerobically [without oxygen present] to aerobically.
This ‘aerobic recovery’ involves tapping into swathes of oxygen to facilitate fat burning. Basically, that energy debt you’ve built up through bench presses needs to be paid back and you do that by metabolising fats.” Essentially, your muscles become a metabolic sink, so you slice through the fatty stuff rather than storing it.
Strength work becomes even more important as you age. A classic 1977 study revealed that resting metabolic rate gradually declines alongside the loss of muscle mass that begins in your 30s. Since then, further research has corroborated those findings.
A 2007 study showed for men aged between 50 and 80, the number of fibres in the large thigh muscle, the vastus lateralis, decreased by 50 per cent, from 600,000 fibres to 323,000. A key cause is dwindling testosterone levels. Thankfully, pumping iron is an anabolic activity, generating higher levels of testosterone and, thus, muscle.
As for what exercises you should focus on, engaging the major muscle groups elicits the greatest testosterone release for a bigger metabolic hit. So you should target the gluteus maximus (aka your major buttock muscle) – the largest muscle in your body – which is engaged by exercises such as squats. Remember: it’s always best to start at rock bottom.
2. Burn brown fat
How did Neanderthals survive cold conditions? It’s a poser that troubled the esteemed anthropologist Theodore Steegmann. After all, animal-hide clothing would provide meagre protection against a fierce winter. Eventually, he found the answer: brown adipose tissue.
“This is a type of fat that sits between the muscle and ‘traditional’ white fat,” says Gonzalez. “It’s packed with more mitochondria than white fat, which means it’s extremely good at burning off excess energy and generating heat.”
White fat provides insulation, but brown adipose tissue is the only mammalian cell whose sole purpose is to generate body heat – a process called thermogenesis. Initially, it was thought that the role of brown fat was important only in babies. One of the many challenges facing newborns is the need to maintain a stable temperature.
With a relatively high surface-area-to-body-mass ratio, they haemorrhage heat. But when core body temperature drops, brown fat can be activated, sucking up white fat and creating heat energy.
As scanning equipment became more advanced, though, it became clear that brown fat plays a part in the metabolism of people of all ages.
So how do you activate your brown fat stores and tap into the thermic metabolic effect? “It’s activated in cold conditions,” says Gonzalez. “Admittedly how it affects our daily expenditure might not be hugely significant, but it could be one benefit of training in the cold.”
You could try cold-water swimming, for example. An analysis of 104 studies concluded this activity could not only significantly increase your insulin sensitivity, but also kick-start your brown fat’s metabolism-boosting powers. If you do fancy an icy plunge, though, do so with a friend and have warm clothes to hand.
3. Increase your protein intake
Protein is key to boosting metabolic health for two reasons: it plays a key role in building muscle and it takes a lot of energy to digest. “The thermic effect of food depends on a few factors, but mainly whether you’re digesting carbohydrates, fat or protein,” says Gonzalez.
“Protein has a much greater thermic effect” – that is, the energy required to digest each macronutrient as a percentage of the energy provided.
“The thermic effect of fats is less than 3 per cent, carbohydrates up to 10 per cent, and protein 20 to 30 per cent. So if you consume 1,000 calories of protein, you’ll expend 200 to 300 calories simply digesting it. That’s why protein is so powerful if you’re looking to cut weight, but maintain muscle mass.”
Protein also stimulates muscle protein synthesis and, hence, muscle growth, improving your basal metabolic health. But it’s not just what you eat that matters. The timing is also important for maximising muscle growth and raising your metabolic foundations.
You should aim to consume protein within an hour of finishing your workout. The optimal intake is around 20g – a pint of milk or four medium eggs, say – though the ideal amount depends on the type, duration and intensity of exercise.
Research led by Luc van Loon, Professor of Physiology of Exercise and Nutrition at Maastricht University, suggests that the lack of muscle stimulation overnight curbs muscle growth. It also showed that consuming protein just before sleeping can increase levels of available amino acids in the blood, improving overnight muscle reconditioning. So a glass of milk, possibly with a spoonful of protein powder, should be your go-to nightcap for a metabolic uplift.
4. Exercise fasted
Strength work is great, certainly, but it’s ideally complemented by cardio work. Not only does variety boost motivation, but more steady-state efforts will also yield metabolic benefits, especially if you train hungry and depleted of glycogen (carbohydrate stores in your body) – heading out for a run before breakfast, say.
“The reason your body adapts to long, low-to-moderate intensity exercise is down to the shock,” says Collins.
“It’s under metabolic stress, and is running out of fuel. So it starts to adjust by increasing blood supply, the number of mitochondria [cellular powerpacks] within the muscle, and the ability to take up and burn fat. In response to this fuel crisis, your muscles become better at taking up and using fuel. This effect is amplified by glycogen depletion.”
As a result of these changes, your body becomes more efficient at using fat as fuel. All of this contributes to raising your FatMax – the exercise intensity at which you burn the greatest amount of fat for fuel.
Research suggests that optimal FatMax is reached at heart rates around 75 per cent of maximum for elite athletes, dropping to around 60 per cent for the rest of us.
Training faster may be a proven fat burner, but do it judiciously – it can strain your immune system. Best start with a 30-minute fasted jog once a week, then add 10 minutes to that session each week until you push it up to an hour. In not too long, you’ll become a vacuum for fat.
5. Play the long game
Your suspicions were right all along: your body is trying to sabotage your weight-loss plans. In fact, any time you’re running a calorie deficit, your body will go all out to try and redress the balance.
If you take in less energy than you use, levels of the satiety hormone leptin will drop – so you’ll feel less full – while levels of hunger hormone ghrelin will rise, stimulating your appetite. As Collins puts it: “There will be strong drivers to down your dieting tools.”
In short, shedding extra pounds through dieting isn’t an easy feat (though the tips in this article will help) – and changes in your metabolism then make maintaining your desired weight a challenge.
Why? As we’ve seen, more body mass means more energy required to function – and vice versa. When you drop the pounds, your body needs fewer calories each day – your metabolic rate will be lower. So what was previously a calorie deficit becomes just the right number of calories to maintain your body.
What this means is that, if you resume your old diet upon reaching your target weight, your waist size will likely sneak back up. The solution? In theory, it’s simple: stick with your new, low-calorie diet even after you hit your goal weight.
Your metabolic rate is lower, so what was once a calorie deficit needs to be your new normal. “It’s all about energy balance – your calories in and calories out,” explains Collins. “It’s about adjusting to a new level and then maintaining it.”
This metabolic biology might sound miserable – who wants to diet forever? Yet, as Collins argues, a simple perspective shift can be powerful. Instead of seeing your journey as solely going from weight A to weight B, view it as a complete lifestyle change – something that will improve your health for decades.
“Holistically, it’s really worth losing excess weight,” says Collins. “This can, for instance, help clear blood lipids more effectively and aid control of blood glucose levels. Both are key when it comes to improving your overall health.”
Adopting these behaviours isn’t just a way to improve your metabolism and shrink your waistline – it’s all a part of becoming a healthier, happier (and, yes, smugger) version of you.