As I spoon 75g of cooked pasta into the triangle of my “portion control” plate, I can’t quite believe how modest it looks. Last week, I would have blithely served myself a ­plateful; then gone back for ­seconds. Now, my life is divided into a pie-chart of shame. 

I exercise a lot, but it turns out I am the queen of overserving. Only now do I realise the extent of my “portion distortion”. According to a chart published by the BDA (British Dietetic Association), my daily allowance of pasta should be a meagre 75g, and cheese should be matchbox-size – oh God, did everyone know that? A serving of meat should be palm-of-hand-size; a serving of fish, the size of a chequebook. Snacks are even more dangerous, of course: a portion of Pringles should comprise just 13 of them. Quality Street? You can have two.

I buy an adult portion-control plate, which helps you work out the right amount of food, in the right proportions (50 per cent salad and veg; 25 per cent high-quality protein; 25 per cent complex carbs), within the 2,000 calories a day that women need and 2,500 for men. It feels like eating from a toddler plate, but is surprisingly effective.

We flatter ourselves that we’re healthier than ever, with our kale and quinoa. But we’re serving ourselves huge portions. The average size of many of our foods, whether from fast-food chains, restaurants or supermarkets, has grown by as much as 138 per cent since the 1970s, according to data from the American Journal of Public Health, the Journal of Nutrition and the Journal of the American Medical Association.

And UK portions are going the way of those of our US friends, as our plates (and drinks) get bigger. 

“Since the 1970s, there are so many more eating opportunities, and a much greater variety of foods available, particularly convenience foods and energy-dense treats,” says Victoria Taylor, senior dietitian for the British Heart Foundation (BHF). “And having a little bit more of something energy-dense makes a much bigger difference in terms of total calories consumed.”

A landmark 2013 study led by the BHF showed portion sizes in the UK have soared over the past 20-30 years. Curry ready meals had expanded by 50 per cent, as had the number of crisps in a family bag. A plain bagel had jumped 24 per cent in size in two decades; biscuits were up to 17 per cent bigger.

And even when we shop wisely, there’s confusion regarding food labelling, says Hannah Whittaker, a registered dietitian and spokesman for the BDA. “It’s generally assumed a prepackaged lasagne serves a single individual; however, this may be a portion for two people. The nutritional information is also generally provided per 100g, while the package contains between 400g-600g. Determining the appropriate portion size can become confusing.”

Restaurants are notorious for serving large portions – about 2½ times larger than standard serving sizes. Factor in bottomless brunches and buffets, and no wonder waistlines are expanding. And watch out for “meal deals”: if you go in for a healthy sandwich but add on a sugary drink and crisps, you’ll add 350 calories.

Of course, supersized portions appeal to the consumerist idea of better “value” – getting more food for less money. “But it’s only now we’re seeing the implications of the changes in our diet over the past 50 years, in terms of obesity and being overweight. So that marketing strategy of generosity is not such a good thing,” says Taylor.

The BHF found nearly nine out of 10 of us pour out more than 30g of cornflakes (the manufacturer’s recommended portion size). The average portion served was 44g – nearly 50 per cent more. And only 10 per cent of people understood that a 200g bar of milk chocolate should give eight portions. 

Whittaker, a specialist in paediatrics and pregnancy, says vegans or those who follow a plant-based diet may also encounter challenges. Mistakes can occur when consuming nut butters and avocados, as one avocado a week is deemed sufficient.

Even home cooks don’t always know the correct serving. “Our research shows people don’t really attend to the portion size on a pack,” says Professor Marion Hetherington of the University of Leeds, who specialises in the psychology of appetite across the lifespan. “People aren’t necessarily aware that they’re eating more because you’ve offered them more.” People tend to eat what you put in front of them, regardless of how much. 

As a psychologist, she’s fascinated by who is most susceptible to the “portion-size effect”. “The people who tend to be most vulnerable are those with a high enjoyment of food, versus someone who eats for fuel,” she says. Many of us are emotional overeaters because we’re lonely, bored or live alone.

Growing up in the West Midlands in the 1970s, we ate three defined meals, sitting at the table. I can remember my father cutting a small pork pie into five, served with salad.

Dessert might be a small bowl of strawberries (picked at the local farm) or Dad’s blackberry and apple “HogPot”. And if you failed to clear your plate, that was it. The larder had a metaphorical lock. 

Later, we acquired a yoghurt maker and a toasted-sandwich maker (retro heaven!). But a packed lunch would only contain a cheese sandwich, a tangerine and a small Club Biscuit. Even when Granny allowed us Angel Delight, she spooned it into small serving bowls to set. Instant portion control.

But we were satisfied with smaller portions. And, sigh, pretty slim. Because this was before “convenience” foods. Shops closed at 5.30pm. Now, thanks to all-night supermarkets and delivery apps, we can eat whenever we want.

So, in a bid to save my waistline, I commit to a week of eating like we did when John Travolta was still hot. I set myself a 1970s-style regime: small portions, no snacks, and eating from smaller plates and glasses.

The psychologist Brian Wansink (the author of Mindless Eating: Why We Eat More Than We Think) has proved that oversized tableware makes us consume bigger portions. A large ice-cream scoop makes you take more ice cream; a short, squat glass more juice. 

In the 1970s, an average dinner plate measured 22cm (8½in) in diameter – now it’s more like 28cm (11in). I also invest in a drinking thimble, so I know exactly what a 125ml (small) measure of wine looks like.

In the 1970s, a standard wine glass held 200ml; today, some glasses hold a third of a bottle. Larger glasses make people feel they’re drinking less, and they gulp faster. 

Our confusion over portion sizes is also linked to the fact we have lost many basic instincts about cooking. We measure by eye; tip the packet. The experts advise me to use tools, a scoop or a spoon, or best of all, my clasped hand, to stop “portion creep”. 

I cook from scratch for the week (homemade has less sugar, salt and fat than cook-chill meals). I grate my cheese so it looks more; carefully spoon my two-egg omelette or salmon onto the correct triangle of my plate. An easy way to measure spaghetti is to use your thumb and index finger to hold a bunch the size of a pound coin.

There’s little in the way of guidance from the Government on ideal portions: information on typical portion sizes hasn’t been updated for more than 20 years. And yet reducing sizes could have a huge impact. According to experts from Cambridge University, if British consumers could avoid outsized portions, they would cut the amount of energy they get every day from food by 12-16 per cent (up to 279 calories).

I can’t say 1970s dining is always easy. I stick to simple meals – with complex recipes it’s harder to work out the portions. I go to bed early because I’m hungry. Friends call it “the martyr’s diet”. But I’m less tired and bloated. I don’t get shattered in the gym. I feel more in control.

In a restaurant, I do the food maths in my head. Normally, I would tuck in – and clear my plate – but now I think twice. I clearly need less food than I think. The hunter-gatherer in me panics before I’m actually hungry. 

No one likes the concept of “less”. We yearn for the overflowing glass and the laden table. But, for now, I’m sticking with my toddler plate. 

Portion-control hacks

Use smaller plates

In one study, people using a large bowl ate 77 per cent more pasta than those using a medium bowl. “I’ve just hosted a Ukrainian family for a year and they always used my side plates, because my dinner plates seemed giant-sized,” says Prof Hetherington.

Drink a glass of water 30 minutes before a meal

This will make you feel less hungry, and help distinguish between hunger and thirst. 

Use your hands as a serving guide

Hands usually correspond to your body size. A rough guide for each meal is – high-protein foods: a palm-sized serving for women; two for men. High-carb foods: one cupped hand for women; two for men.

Order a half portion when eating out

You could share a meal with a companion, or order a starter and side dish instead of a main. 

Chew slowly

It can take 20 minutes for our brain to register that we are full.

Plate up first, rather than serving food directly from the stove

This will prevent overfilling your plate and discourage returning for seconds.

The Telegraph