Whether you’re trying to ditch some excess weight, shed those post-baby kilos, or get in shape for the fun run marked on your calendar, you’re probably monitoring your progress by stepping on the bathroom scales. And while it’s easy to rely on that magic number, it turns out that your body weight doesn’t tell the full story.
It’s more important to understand your overall body composition – your lean muscle mass and how much fat you’re carrying – because what you’re really trying to lose is fat. But trying to obtain an accurate measure of fat and muscle composition is a bit like trying to figure out how much butter you put in a cake after it came out of the oven. So what’s the solution? Most experts recommend using several different measuring tools to help you understand what your body looks like and how to achieve your goal – because one size certainly does not fit all.
Our bodies naturally variate
The obvious problem with jumping on the scales every morning is the reading doesn’t take the body’s natural variation into account. “Body weight fluctuates anywhere from 0.5 to two kilos a day depending on a person’s body weight and size,” says Dr Nick Fuller from The Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders at the University of Sydney.
“If your weight goes up and down from day-to-day, it might not be true weight loss but changes in your hydration levels or water retention in the body because of a different meal or food product. If you had a meal that was high in protein and low in carbohydrate – which retains very little water – it might look like you’ve lost weight but that might not be the case. The opposite may be true of a carbohydrate-rich meal.”
Sine McGregor, an accredited exercise physiologist at Kaizen Exercise Physiologists, says that everything from what time of the month it is, to whether you have food sensitivities or excess fluid retention can impact on that humble little number on the scales. “If you’re just looking at the scales you’re only getting a small piece of the puzzle of how the whole system is working together and how well it might function,” says McGregor. “It’s a really, really small part of a big picture.”
Muscle weighs more than fat
Ordinary bathroom scales miss the mark because they’re unable to separate the weight you want to lose (fat) from the weight you want to retain (muscle). Losing fat and building lean muscle with dietary alters and exercise changes the overall composition of the body, helping it become healthier and more efficient. Why? Because muscle burns fat. Rather than striving for a number on the scales, women aged 20 to 59 should aim for a body fat percentage of around 21 to 34 per cent.
Personal trainer, Deanna Giuliani says the scales are especially deceptive because muscle weighs more than fat. “Fat is equivalent to 900 grams per 1.1 kilograms of muscle, so even though your size will change with weight training, it will usually go towards the muscle, which weighs a little bit more,” she says. “However, the more muscle you have, the more energy your body needs to burn to keep your metabolism going, which helps you to lose fat. If you want to reduce your thighs, for example, you’re aiming to gain a little bit more muscle because the fat will decrease, which means the thighs will reduce.”
Exercise physiologist, Dr Bill Sukala agrees: “The scale by itself isn’t an effective measure of weight loss. It will tell you the weight but not the composition of that weight. For a woman who weighs 75 kilos, if she’s very tall or short that’s going to make a difference to the proportions. Or one person may have more muscle and another person may have less muscle and more fat, so you have two people at the same weight but in fact one is very fit and lean while the other is low in muscle and high in fat.”
If you’re solely relying on the scales, it’s easy to be lured into a false sense of weight loss. “You want to be losing weight from body fat stores and preserving muscle mass,” says Dr Fuller. “Weight may go down over time, but if that’s just related to a change in fluid level in the body that won’t be reflected in changing body fat.
“Looking at body fat change over time is potentially a better indicator of whether you’re actually losing weight. Even better, if you can look at the change in body fat to muscle ratio, you can see if the weight loss is coming from fat or muscle stores or a combination of both. Often it will be a combination but we want to be seeing most of the weight coming from a loss of body fat not muscle.”
The best way to measure improvements
If the scales aren’t a good choice, what should you use instead? The most common measure of body fat and associated health risks is body mass index (BMI). It relates weight to height and provides an indication of whether you’re underweight, overweight or an ideal weight for your height. While the BMI model is used by the World Health Organisation, the Heart Foundation and the Cancer Council – largely because of its ability to provide accurate measures at a population level – it suffers from the same major flaw as the scales as it can’t distinguish fat from muscle.
Waist circumference is often touted as a better predictor of health risk than BMI because having fat around the abdominal organs means you’re more likely to develop obesity related health conditions like heart disease, type 2 diabetes and high blood pressure. For women, a waist circumference of 80 centimetres or over indicates an increased risk.
But, of course, measuring your waist doesn’t measure changes in overall body composition so many folks turn to body fat scales, which send a low electrical current through the body to measure fat and muscle mass. Tissue that contains a lot of water – such as muscle – lets the current through easily, but fat contains comparatively little water, so it resists the current. Therefore, the higher the impedance, the more fat there is in the body.
Building on the same principles, a DEXA (dual energy x-ray absorptiometry) scan – two very low doses of x-ray that pass over the body from head to toe – is the gold standard of measuring body composition.
“DEXA provides an accurate indication of how much lean mass you have, which is your muscle and bone, and also how much fat mass you have,” explains Dr Sukala. “It can tell you not just how much fat, muscle and bone you have but exactly where it’s located. It will give you a breakdown of, for example, how much fat, muscle and bone you have in your right arm, left leg and torso.”
Dr Sukala says the real value of DEXA is its ability to reliably detect very small changes in body fat over time. “In a 12-week challenge you could get a scan at the beginning and another one at the end of 12 weeks, which gives an accurate indication of what’s happening in the body.”
But accuracy doesn’t come cheap, with DEXA costing up to $150 per scan. If it’s not in your budget, most experts recommend using the other measurement tools in combination. It’s especially important to use them consistently – at the same time of the day and month, and in the same clothes. “Look at a combination of analysis techniques to see what’s happening over time, focusing on body fat loss rather than seeing the weight loss come from muscle,” adds Dr Fuller.
In the gym, McGregor encourages incorporating regular strength training into your workout regimen. “With weight loss, the research is saying that you’ll lose 70 per cent body fat and 30 per cent muscle mass, so it’s important to maintain strength training and muscle mass while trying to lose weight because that muscle mass tends to come off as well.”