You've been eating fewer kJs, you see your trainer more than your best mate, and you're definitely trimmer. But now it seems you couldn't lose a kilo unless you cut your arm off. You've hit the dreaded plateau.

"At a certain point, usually after losing about 10 per cent of your weight, you may have to tweak your diet and exercise to jump-start your body," says Dr Susan Mitchell, dietitian and author of Fat Is Not Your Fate.

Here, why you might stall and what you can do to rev back up:

You're eating for 75 (kilograms, not people)

Flatline Yeah, losing mass means you look better in your low-riders, but it also means there's less of you to burn kilojoules. It's a cruel truth: your basal metabolic rate (BMR) - the number of kilojoules your body needs just to exist - gets lower as you get littler. Keep eating for your old weight and you're going to hit a wall.
Finish line As the number on the scale goes down, so too must your food intake. To (roughly) figure out your BMR, multiply your current weight by 101.32 to get your basic kilojoule needs (how much your body burns just by existing). Now multiply your BMR by 1.2 and voilà, you've got the average number of kilojoules your body burns per day when you factor in normal activities (on days you do an hour of moderate to intense exercise, add another 1250 to 2100kJ). Once you have your final number, shave off 2100 to find out how many kilojoules you need to eat to lose half a kilo a week, or 1250 to lose a kilo a month. Just don't ever go below 5025kJ a day or you'll run into the problem below.

You're eating for 45

Flatline Here's the surprising flip side: there's such a thing as eating too little to lose weight. "The body needs a certain number of kilojoules per day to meet minimum metabolic needs, such as cardiovascular function and respiration," Dr Mitchell says. When you're running on empty, your brain sends signals to various organs (like your thyroid), telling them to slow down your metabolism and conserve energy.
Finish line The best strategy? It's simple: "Increase your kilojoules," Dr Mitchell says. "Many women are afraid to do this because they think they'll gain weight, when actually the body will function more efficiently and they'll start losing again." If you're stuck (and starving), try adding 420kJ a day for two weeks.

You've become an exercise fanatic

Flatline So you've amped up your workout. Great! Now you have to give your body time to recover. If you don't schedule any downtime, the kilos won't budge. "When you're sore after a workout, it's because you've torn the muscle fibre," explains Angela Corcoran, a personal trainer. "When you rest, the muscle fibre has a chance to heal and comes back more effectively. This drives up metabolism, so you burn more kilojoules at rest."
Finish line Take a day off! Corcoran says she has seen clients lose weight after they've logged a few days of rest. But this doesn't mean you get a week to bum around watching daytime telly (nice try), 24 to 48 hours is all your body needs to recover. Cassandra Forsythe, a nutritionist and exercise scientist at the University of Connecticut in the US, suggests working out two consecutive days followed by a day of rest, taking no more than three days off in a row. (You've been warned.)

You could work out in your sleep

Flatline Been repeating the same moves since New Year's? You need a kick in your (shrinking) behind. "When your body is used to an exercise, it stops making physiological changes," says Forsythe. Translation: your body has become so efficient at doing your current routine that it's burning fewer kilojoules. Want proof? A recent study in the International Journal of Obesity found that runners who didn't increase their mileage gained weight over time.
Finish line Mix it up. "To grow more muscle and keep your metabolic rate high, you have to damage the muscles a little by challenging your body with a different workout," Forsythe says. If you're a treadmill rat, get on the elliptical or bike. If you're hell-bent on the treadmill, up the intensity (by adjusting the speed or incline) every other minute, or work up to a longer run, adding a kilometre every couple of weeks. In the weights room, forget those 15 reps you usually do with a 2kg dumbbell: "Decrease the reps and increase the weight, using one you can lift only five to eight times," Forsythe says.

Your body baulks

Flatline Like it or not, you have a "set point," Forsythe says - a genetically determined weight where you're most comfortable. To stick to this number and regulate its fat stores, your body uses a gazillion physiological mechanisms, like interactions between hormones and molecules that affect hunger levels. So if you're trying to drop 10 kilos below your set point, you're getting in the ring with Ma Nature. When you don't eat enough to maintain your set point, your body thinks you're starving and "responds by lowering its metabolic rate, which in turn reduces the number of kilojoules you burn," Forsythe explains.
Finish line The best way to conquer your set point is to speed up your metabolism with regular exercise - at least 30 minutes of cardio, five days a week. It also helps to increase the amount of good fats (such as monounsaturated) and lean protein (think fish and poultry) in your diet - these foods can accelerate your metabolism.