Many of us believe that taking exercise gives us a licence to eat fattening foods with no adverse effects. Surely that's the whole point of physical exertion? Not so, say the experts. Any effective exercise habit must be supported by the right food. "It's like fuelling a car," says sports scientist Dr Garry Palmer. Bad nutrition, he says, can hinder performance, leaving you sluggish and nauseous and, eventually, making you ill.
"Many people think going to the gym means they can eat what they want. It can free you up, but not much," says sports nutritionist Drew Price. "It depends how overweight you are."
Heidi Skolnik, a sports nutritionist who works with the New York Giants football team, says it is all about balancing the calories coming in with the calories going out. "I often see people who can't understand why they're not losing weight, but when we look at their food intake, they're eating as if they're running a marathon, not half an hour a day. That might burn 300 calories, but that's one chocolate bar - not a lot of food. Generally, you need more calories only if you are training intensely for more than two hours every day."
The standard advice is that, if you're exercising, your diet should consist of 60% carbohydrates and 10-12% protein. The rest should be fat. If you want to lose weight, eat more protein and reduce both your carb and fat intake. "Proteins increase your metabolism and chew up calories faster," says Price. Other pound-shedding advice is to eat your carbs in the morning or immediately post-exercise, when they are less likely to turn to fat. Skolnik says sipping a carb-based sports drink during an intense spinning class (lasting an hour or more) increases blood sugar levels and helps the body to burn more fat.
"Whatever your goals, the most important thing is to make sensible food choices," says Price. "That's good quality protein (lean meat, fish, tofu, soya mince, quorn, quinoa, low-fat cottage cheese or quark cheese), good fats (oily fish, walnuts, flax seeds or flax-seed oil) and good carbs (wholegrain rice, bread and pasta, sweet potatoes and oats)." As we know, not all carbs were created equal. "Good carbs have a low glycaemic index - glucose is released slowly into the blood - and won't result in energy crashes," says Price.
Another piece of well-known, but often ignored, advice is to drink enough water. "One study showed that almost half of all gym-goers were dehydrated before they even started exercising," says Skolnik.
Tess Griersmith, sports dietician at the London Sports Medicine Centre, says that even mild dehydration can impair performance by 30%. Some studies advise that you drink just under three litres a day when exercising, including half a litre two hours before physical exertion. "Check you are getting enough by weighing yourself before and after," says Skolnik, then drink half a litre for every pound lost while working out.
The timing of meals is also a big factor. The general rule is to wait three to four hours after big meals and one and a half to two after smaller meals before exercising. This way you'll avoid feeling lethargic or nauseous.
Bear in mind, however, that everyone's needs are different, depending on your fitness regime and body composition. Serious number-crunchers can calculate their basal metabolic rate (BMR), the number of calories they would burn if they stayed in bed all day, and from there, work out their calorie needs based on activity levels (try an online BMR calculator such as bodybuilding.com/fun/issa64.htm).
Alternatively, keep a food diary, noting down everything you eat. It is hard to kid yourself when it is all there in black and white. Above all, says Price, see the bigger picture: "There are no bad foods, just bad times and quantities to eat them in."
The morning workout
Early birds need to pep up their blood sugar, refuel their muscles and drink around a pint of water to replenish the water lost during sleep - remember, your body has been on an eight-hour fast. "Dehydration is one of the biggest factors in morning workouts," says Price.
Some people can exercise on very little, but if you love breakfast, aim for a small but healthy one - such as oats, yoghurt and fruit or brown toast with a little jam - no less than an hour (preferably longer) before you work out. Think little portions: exercising on a full stomach will only make you nauseous.
Breakfast refuseniks can up their blood sugar with half a banana or half a slice of bread before they work out, and then eat a healthy breakfast afterwards such as fruit, oats, wholemeal toast and a poached egg washed down with a pint of water. Is it ever OK to exercise on an empty stomach? It depends on the individual. Dr Palmer recommends that, for intensive workouts, the athletes he works with delay the solids and opt for a pre-exercise sports drink instead.
The lunchtime workout
It is nearly one o'clock, your stomach is growling, but you are determined to hit the gym. You can't eat lunch before a workout, so, ideally, you should snack on some fruit, nuts and yoghurt at "around 10.30-11am to stabilise your blood sugar," says Price. "Then have lunch after you've exercised."
If you're too busy to remember to do this, nibble a banana or raisins right before you exercise. Sports drinks are advisable only if you are doing high-intensity exercise or working out for more than an hour, otherwise you will be saddled with spare calories. A quick cuppa can help (30-45 mins before), but have tea or regular coffee, not a double caramel latte.
"Caffeine is a double-edged sword," says Price. "It allows your nervous system to fire more easily so you can do more work without feeling it. But too much of it can dehydrate you." Sensible post workout lunch choices are a chicken or salmon salad or sandwich, veggie bean tortilla, or tuna and a jacket potato, plus fruit.
The after-work workout
Dodge the afternoon munchies by eating a yoghurt and fruit around 3-4pm. This fuels the body ready for your evening workout, and keeps your blood sugars up so that you won't be ravenous by dinner and therefore more likely to overeat. Skolnik advises eating a small carb snack immediately after your workout, particularly if you have a long journey home (fitness lore states that you should eat or drink carbs 15-30 minutes after exercise to repair the muscles).
For dinner, have lean protein and plenty of colourful veg, such as salmon with stir-fried vegetables and wholegrain rice or pasta; pasta with chicken breast and steamed or roasted vegetables; chicken and vegetable couscous, or lentil-and-bean tabbouleh with vegetables. Avoid eating a mountain of pasta, for example, and loading your body (and waistline) with carbohydrates. Again, make sure you drink enough water - especially if you're drinking alcohol.
