Dietitian Claire Turnbull answers your most commonly asked questions about food, drink and exercise.
Q: Will you burn more body fat when you work out on an empty stomach?
If you are exercising before you eat breakfast, then technically, yes – you may burn more fat as fuel, simply because your body’s stores of its preferred fuel, glucose, have been depleted overnight.
But we wouldn’t recommend it. Exercising on an empty stomach can limit the time and intensity of your workout, so you don’t burn as many kilojoules – and thus, you don’t burn as much fat. Having something to eat beforehand will help you work out harder and longer (so you burn more kilojoules). This can also help you achieve a higher level of fitness, faster, which may in turn result in your future workouts being more effective – so you burn even more kilojoules! Our verdict: eat up.
Q: I do a lot of weight training. Should I be eating protein bars or drinking protein shakes?
Protein bars and shakes can be a convenient snack after a workout, and if you are weight training heavily you do need to increase your protein intake (aim to eat 1.2–1.7g protein per kilogram of your body weight each day). But, in most cases, protein supplements aren’t necessary. Australians generally get enough protein from everyday foods, like lean meat, chicken, fish, dairy products, eggs, nuts and legumes. Plus, these foods have extra ‘goodies’, such as iron, calcium and healthy fats.
Q: I swim every morning for at least an hour. Can you suggest what I can eat afterwards, on the way to work, to give me the nutrition I need?
After morning exercise, rehydrating and eating a good breakfast are a priority. Along with lots of water or a sports drink, a snack that is a mixture of carbohydrates and protein is ideal. Try a low-GI breakfast cereal with some protein, such as oats with a banana or some berries and some yoghurt, to help keep you going until morning tea. Other good options include having a peanut butter and banana sandwich, a low-fat yoghurt and a piece of fruit, a fruit bun and flavoured milk or an Up & Go.
Q: Are all sports drinks the same? And are they better than water?
Sports drinks, such as Powerade and Gatorade, have been cleverly designed to have just the right amount of carbohydrates (5–8g/litre) and electrolytes to keep you well hydrated. They are a good way to keep your body fuelled and hydrated, if you’re exercising at a high intensity for more than 90 minutes. But for shorter, less intense sessions, plain water will do the job just as well and doesn’t contain unnecessary kilojoules.
Q: I get cramps in my calves. Do I need more salt?
Maybe – sweating heavily during exercise can result in low blood salt (sodium) levels, which are associated with cramps. But don’t start sprinkling salt on your food just yet – the most common reason for muscular cramps is actually dehydration, not salt.
If you’re suffering from cramps regularly, start by drinking plenty of fluid before, during and after training to minimise your risk of dehydration. Sipping on a sports drink might be a good idea, too, as these can help replace salt (sodium) losses as well as rehydrate you. Finally, try stretching and massaging the cramped muscle to alleviate the pain, and use the opportunity as an excuse to have a soak in the bath – these actions can help aid a faster recovery.
Q: To shift some weight, I have just started doing exercise. Will cutting down on carbs help, too?
Yes. The best way to get your weight down is to focus on reducing portion sizes, alcohol and high-fat foods, and being active. Reducing portion sizes means cutting down on protein, fat and yes, carbohydrates – particularly if you’re serving yourself generous amounts! Of course, it’s still important to make sure that you’re getting enough of these essentials. Carb-rich foods, such as bread, pasta, rice, potatoes and cereals, provide much- needed energy, fibre, vitamins and minerals, and carbs have an energy density similar to protein and lower than fat. Don’t be afraid of them!
Q: Which exercise burns the most fat – running or walking?
If you’ve been to the gym recently, you might have seen the ‘fat burning’ setting on the treadmill – a gentle-to-moderate speed, where you walk (not run) to burn fat. Technically, you will burn more fat when you’re walking – it’s true. But if you want to lose body fat, don’t swap your morning jog for a gentle stroll just yet.
Your body burns different fuel sources when exercising at different intensities. When you’re doing a low-intensity exercise like walk ing (when your heart is beating at less than 60% of your Maximum Hear t Rate – see below to work out your MHR*), almost all of the energy you burn is from fat. As you start to increase the intensit y – say, to a hard walk or a jog (60–80% MHR) – you keep burning fat, but your body begins to burn its store of carbohydrates, as well. At a high intensity, like sprinting (greater than 85% MHR), carbs become the most prominent fuel source used.
So walk ing might burn the most fat, but it doesn’t burn the most overall energy – and that ’s what you need to focus on if you want to lose body fat. Here’s where higher intensity workouts, like running, come in – they get your heart rate up higher, burning more overall energy than walking would if you do them for the same length of time.
Walking is still a worthwhile ‘fat loss’ exercise, of course – you will eventually burn the same amount of energy as you would doing a shor ter, higher-intensity workout. But you’ll have to exercise for twice as long to burn the same amount of energy.
In addition, research has also shown that you can burn more fat – and burn fat for longer after your workout – by ‘interval’ training: exercising at alternating intensities. Simply choose a favourite cardio activity (including brisk walking) and alternate between vigorous and slower movements every 60 seconds. Stick to this consistently (and don’t forget the healthy, kilojoule-controlled diet!), and you’ll start to see results.
*Maximum Heart Rate = 220 beats per minute, minus your age.