How and what to eat at Christmas without gaining weight? Christmas Eve can be a moderate evening

An index that not only investors should be watching

Christmas Eve, Boxing Day, New Year's Eve are coming, people want to treat themselves, they plan in advance to overeat over the holidays and then work it all off afterwards. Plenty of sweets and cakes will have a medium or high glycaemic index, which tells us how quickly the carbohydrates we eat get into the blood.

How is the glycaemic index calculated?

Bodybuilder Rasťo drinks 50 g of glucose (a simple sugar) and we measure how long it takes to reach his blood. That will be our baseline value of 100.

Rasťo then eats a meal containing 50 grams of carbohydrates and again we measure how quickly they're absorbed into his blood. The glycaemic index is then a number from 0 to 100 expressing where a food sits on the scale according to how fast its carbohydrates are absorbed into the body compared with glucose.

On every nutrition table you'll find the entries Carbohydrates and Of which sugars. Complex carbohydrates are made up of simple carbohydrates – sugars, which consist of one or two molecules and are therefore easy to digest.

When you eat a complex carbohydrate, it takes longer for it to be broken down gradually into the tiny molecules of simple sugars that you can digest.

After a meal the pancreas produces insulin, which carries the sugar from the food into the cells. Ideally, there shouldn't be big swings in carbohydrate intake over the course of the day, and therefore none in insulin levels either.

How do you lower the glycaemic index?

If you eat some protein, fat or fibre along with your carbohydrates, they'll help slow down their digestion. Foods and drinks with a low pH also delay the rise of glucose in the blood. Portion size matters too, of course. Christmas Eve can be a moderate evening – or rather, we've got one hack for you.

In one study people ate the same breakfast, lunch and dinner, but one group ate the whole dinner at 9 p.m., while the other had dinner split into two parts. At 6 p.m. they ate a portion containing 70 % of the carbohydrates and at 9 p.m. they ate the rest.

Splitting the meal into two small portions with a lower glycaemic load, three hours apart, resulted in lower blood glucose compared with eating the whole portion in one go.

So if you split your food into smaller portions, your blood sugar won't be going off like firecrackers in the street.

The way food is prepared matters as well. For example, 100 g of boiled potatoes has 16 g of carbohydrates and a glycaemic index of 60, while 100 g of baked potatoes has 20 g of carbohydrates and a glycaemic index of 80.

It's not just about the load on the Olympic bar

The glycaemic index, however, doesn't tell you how high blood sugar will go after a meal or how long it will stay up. That's what the glycaemic load is for – it reflects a food's effect on blood sugar better and more realistically.

The glycaemic load tells us how fast and how large an amount of carbohydrates we get into the body from one portion of a carbohydrate meal.

For example, watermelon has a glycaemic index of 75, which is fairly high, yet a 100 g portion has a glycaemic load of only 4, because it contains just 6 g of carbohydrates per 100 g. In short: it's not a complete disaster if a food has a high glycaemic index. What also matters is how much carbohydrate the food actually contains.

Experiments have confirmed that eating a meal with a low glycaemic index rather than a high one lowers blood glucose by as much as 40 %, while keeping the same amount of energy in a single portion.

This is influenced by the ratio of protein, fat and carbohydrates. In this experiment the energy coming from fibre was increased and at the same time the energy from carbohydrates was reduced by 10 %.

If you eat a meal that gets 42 % of its energy from carbohydrates and 7 % from fibre, you'll end up with lower blood sugar than if you eat a meal where carbohydrates make up 65 % and fibre 1 % of the energy.

Changing the glycaemic load, that is, changing the amount of carbohydrates you take in per portion, affects your blood sugar.

In another study, the first group ate a low-carbohydrate breakfast in which carbohydrates made up 10 % of the energy. The second group had a breakfast where carbohydrates accounted for 55 % of the energy consumed – in line with standard dietary recommendations. Lunch and dinner were the same for both groups – identical nutrient composition. After breakfast, blood glucose in the people who ate the low-carbohydrate breakfast was 74 % lower, and their overall 24-hour blood glucose was lower too compared with the group that had a more carbohydrate-rich breakfast.

This means that even having just one low-carbohydrate meal a day has a positive effect on your overall blood sugar throughout the whole day.

Cheers – with something alcohol-free!

According to the renowned journal The Lancet, the only amount of alcohol that is safe for your health is zero. And if you do decide to drink, drinking less is better for your health than drinking more, and women should drink less than men. But you know that already.

Besides the fact that drinking alcohol is linked to higher mortality,

• Even small doses of alcohol before sport reduce performance – gluconeogenesis drops and lactate production rises, and lactate is what gives us cramps.
• Alcohol increases urine production. 10 g of alcohol increases urine output by 10 ml, which has an adverse effect on recovery from dehydration (e.g. after running or any other effort that makes you sweat).
• Alcohol reduces protein synthesis in the muscles, even when your protein intake is sufficient. Alcohol increases production of the hormone cortisol, which drives protein breakdown.
• Alcohol lowers the amount of glucose in the blood, which has a negative effect on post-workout recovery.
• Drinking alcohol results in a loss of the strength you gain from resistance training.

Our advice: have a tasty protein shake or quality supplements instead of alcohol and you'll see how your body thanks you.

The American College of Sports Medicine has issued a recommendation for those who can't give up drinking: don't drink for at least 48 h before sport, rehydrate first after exercise and eat something before you drink alcohol so that its absorption is slowed down.

And a few practical tips to finish:

If you add honey and lemon to your tea, wait until it has cooled down a bit first. High temperatures break down the very substances you're putting in there for.

If you do manage to overeat, go for a walk. Lying down after a meal isn't a good idea – the best thing you can do is keep moving and get some fresh air.