If you’ve ever stood on the scales and not liked what you’ve seen, here’s a crumb of comfort.
The truth is that more than half of your body weight is unrelated to anything you may have eaten.
It is actually the weight of parts of your body — from your heart to your muscles and even blood.
But these weights can fluctuate, even on a daily basis. And these changes can reflect the state of your health, as this fascinating guide to your body weight reveals…
The truth is that more than half of your body weight is unrelated to anything you may have eaten
Water weight is the main reason why your weight varies throughout the day.
‘Around 50 to 70 per cent of a man and 40 to 60 per cent of a woman is water,’ says Abby Coleman, a sports scientist at Precision Hydration.
So, if you weigh 150lb (68kg) as a man, then 75lb to 105lb (34kg to 48kg) of that could be water; and in a woman of the same weight, it’s 60lb to 90lb (27kg to 41kg).
‘The variation depends on your ratio of muscle to fat, as muscle contains more water, mostly because glycogen [a sugar that is stored as fuel for the muscles] is bound to water,’ she says.
‘That water is then split broadly into that which is outside our cells [known as extracellular fluid, which is the watery part of your blood and the fluid that bathes your cells], and intracellular fluid, which is found within the cells.’
We constantly lose water throughout the day in urine, breath and sweat — and gain it by eating and drinking.
The food you eat can also affect how much water you gain or lose. Cut out carbohydrates and you’ll lose a lot of water weight because you’ll draw on the glycogen stored in the muscles to fuel them. As you reduce these stores, fluid levels fall.
Eat more carbs and you’ll replenish your glycogen — and fluid — stores. Consuming excess salt also sees you retain water.
‘That’s why you might weigh 4.4lb (2kg) more after a weekend of enjoying alcohol (which contains high levels of sugar and other carbs) than you did the previous Friday,’ says Arj Thiruchelvam, a sports scientist from Performance Physique in Birmingham.
‘But by Wednesday your weight should be back to normal as you would have lost this excess water again.’
Overnight, you continue to lose fluid. In fact, it’s estimated that we can lose 3lb (1.4kg) of fluid a night, which is why it’s suggested you weigh yourself first thing in the morning, as you’re at your lightest.
The eight to ten pints of blood in the average adult make up around 7 per cent of total body weight. So for someone weighing 150lb (68kg), that would equate to around 10.5lb (4.8kg).
The amount you lose if, say, you cut yourself, isn’t likely to make a notable difference on the scales — but blood donation might. According to the NHS Blood and Transplant service, the average blood donation takes around 470ml (just under a pint) of blood — which weighs around 1.1lb (499g). It won’t stay gone for long, though — your body makes around two million red blood cells per second and it’s estimated that those removed during donation are replaced within 48 hours.
Weight changes during a woman’s period aren’t due to blood loss: the average woman loses just 30ml to 40ml of blood during her period, around 30g to 40g in weight. The gain is due to fluid retention caused by the pre-menstrual rise in the hormone progesterone.
The skeleton makes up about 15 per cent of your total body weight — so, if you weigh 150lb (68kg), then your bones would account for around 22.5lb (10.2kg) of that.
Interestingly, 25 to 31 per cent of the weight of bones is actually water, and it’s believed it helps nutrients move around the bone.
The rest is calcium and the protein collagen, which make up the bones and bone marrow.
And there is such a thing as being big boned: overweight people tend to have larger, heavier bones, as moving a heavy body creates stress that makes them grow.
Osteoporosis will cause bones to become less dense and lighter, though it’s unclear by how much.
The skeleton makes up about 15 per cent of your total body weight — so, if you weigh 150lb (68kg), then your bones would account for around 22.5lb (10.2kg) of that
Our skin makes up a sizable 14 per cent of the body’s weight. The taller or larger you are, the more skin you have. For someone weighing 150lb (68kg), roughly 21lb (9.5kg) of that will be skin.
However, the skin regenerates roughly every 28 days. As part of this process, according to a study published in 2011, every hour you lose 28mg to 85mg of weight in skin flakes.
If that makes you feel squeamish, here’s some good news: a type of oil, called squalene, in these skin flakes absorbs the gas ozone in the air. This reduces levels of indoor air pollution in your home, according to U.S. researchers from the University of Medicine and Dentistry of New Jersey.
Muscle mass makes up 40 to 50 per cent of your body weight. Some of this comes from the weight of organs such as the heart and lungs, which are mostly muscle, but the vast majority is in fact skeletal muscle (so-called because it’s muscle mostly attached by tendons to bones of the skeleton) — for example, the biceps, triceps, abdominals and glutes.
Interestingly, the more muscle you have, the more you might weigh, but the smaller you will look.
‘Muscle is defined and dense so 2.2lb (1kg) of muscle will spread over a smaller area than the same amount of fat,’ explains sports scientist Arj Thiruchelvam. The exact amount of muscle you have depends on age (we lose muscle as we age); sex (men have more than women); and how much exercise you do.
‘Aerobic exercise — such as running and swimming — will increase muscle in the lungs and heart, whereas resistance exercise — such as lifting weights — also increases skeletal muscle,’ he says.
The muscles become more efficient at handling exercise, though, and build less the more you do.
‘That’s why you should always challenge yourself,’ he adds.
The more muscle you have, the more you might weigh, but the smaller you will look
Fat is found all over the body. ‘Its main job is to insulate the body from cold and protect the organs,’ says Arj Thiruchelvam.
Subcutaneous fat is the stuff under the skin — it’s what you can pinch around the arms, tummy, thighs and buttocks.
Visceral fat is stored around the main organs, and is more harmful because it releases inflammatory compounds linked to heart disease, type 2 diabetes and, potentially, some cancers.
A healthy amount of body fat for the average 40 to 50-year-old man is 11 to 21 per cent; above 34 per cent is obese.
For a woman of that age, it should be 23 to 33 per cent; 40 per cent and above is obese.
‘The body is in a constant state of flux, and its weight is always being lost or gained,’ explains Arj Thiruchelvam.Head — 8%
Head size is largely genetic, with nine known genes associated with it, so blame your parents.
But while men’s heads are slightly larger than women’s, on average the adult head — including the skull, brain, teeth and tongue — weighs 12lb (5.4kg).