How to stay in shape and still enjoy your Christmas dinner.

The chocolate-accompanied countdown to Christmas is really more of a build-up: dinners, parties, end-of-year deadlines, last-minute gift buying, mince pie-tops bulging over your trouser waistband, bags under your eyes. The combination of excessive eating, drinking and stressing, with insufficient exercise, nutrition and sleep can easily result in a body transformation reminiscent of Mr Tim Allen’s metamorphosis in The Santa Clause.

You don’t want to allow the festivities to derail your exercise regimen so much that you require the full-scale intervention of a New Year’s resolution to get back on track. At the same time, you don’t want to be a Scrooge, bah-humbugging miserably in an empty gym of an evening when everybody else is out making merry. And early-morning physical activity is not exactly compatible with late-night revelry and eggnog hangovers.

The solution is everything in moderation: eating and drinking, of course, but also exercise. ’Tis not the season for a punishing session of high-intensity interval training if you’ve just had a bigger night than Kris Kringle’s Christmas Eve. But if you’re mindful, listen to your body and follow these expert tips, you can still offset some of the calories – and alcohol.

Try filling your stomach with less calorific substances. “Try to drink between 500ml and one litre of water in the hour before the meal,” says Mr Matt Gardner (mattgardnernutrition.com), a performance nutritionist who variously advises Rouen rugby club, The North Face and Nuffield Health. Then start with the less energy-dense foods on your plate, usually vegetables, leaving starches and fats to last. Yes, yes, we know – this isn’t really in the spirit of Christmas dinner, but you’ll thank us for it come six o’clock, you really will. The idea with this strategy (keep it from your Auntie Doreen, though – she’ll probably just laugh) is that you’ll be less inclined to over-indulge on meat and potatoes.

Put down your fork between mouthfuls or take a sip of water. (Aim to sink another 500ml while eating.) As for booze, Mr Gardner recommends a spirit with a calorie-free mixer, which is roughly half as calorific as a pint of beer or 250ml glass of wine: “No need to top up with extra liquid calories.”

Unless you’re in hospital for drug addiction, then detoxing, like Santa Claus, doesn’t exist. So if you haven’t been a good boy, morning-after triage is largely limited to drinking water (not too much too quickly or you’ll irritate your stomach more) or fruit juice (fructose helps metabolise alcohol) with a Berocca (to replace lost B vitamins) and ibuprofen (paracetamol and aspirin can cause more upset). Greasy food only delays alcohol absorption, so it’s no good allowing yourself a morning fry-up. Slow-release carbs are better – they will boost your blood sugar and mood, so have eggs on toast (eggs contain liver-assisting cysteine), asparagus (which accelerates the cells that break down alcohol) and bacon (scientifically proven to alleviate hangover symptoms by Newcastle University).

Training is yet another potential stress on your already over-burdened body. “Adding that on top of recovery will set you up for failure,” says Mr Carl Martin, personal training manager of Equinox’s UK clubs. “On the flip side, if you feel good, you can create the space to burn those excess calories.”

Auto-regulate yourself with Mr Martin’s circuit of goblet squats (12 reps), single-arm dumbbell rows (12 reps), dumbbell reverse lunges (12 reps), press-ups (15 reps), plank shoulder taps (20 reps) and dumbbell bicep curls (12 reps). Really energetic? Lift the most weight you can, resting 20-30 seconds between exercises, for maximum muscle building. Hanging like mistletoe? Halve the weight and rest after each round for a lighter, steadier workout. Either way, do 4-5 rounds if you’re up to it – and jingle dumbbells all the way.