Britons are being urged to cut their meals to just 1,600 calories a day and 200 calories for snacks in tough new health guidelines.
They will be told they should limit themselves to 400 calories for breakfast, 600 for lunch and 600 for dinner, reports the Daily Mail.
This comes to 1,600 calories, well below the current recommended daily intake of 2,000 calories for women and 2,500 for men. Those who exercise regularly can have even more.
People who follow the new guidelines can also eat two healthy snacks of up to 100 calories each.
The suggestions from Public Health England (PHE) do not include drinks, but snacks and healthy hydration are likely to keep the total below the current recommendations.
PHE, which is the Government agency for preventing ill health, claims they are merely a 'rule of thumb' rather than strict limits.
Officials claim the average adult is overeating by 300 calories a day, and this so-called 'calorie-creep' is leading to a steady weight gain. But Tam Fry, of the National Obesity Forum, said: 'This is a panic measure to get the public to understand they are eating too much.
"Portion sizes are getting bigger and bigger and people are mindlessly eating them just because they are there. The idea is sound because we are eating too much, but my feeling is the thresholds are too low."
Christopher Snowdon, head of lifestyle economics at the Institute of Economic Affairs think-tank, added: 'It's been well established for decades that reasonably active people need between 2,000 and 2,500 calories a day to maintain their weight.
"Public Health England's latest calorie guidelines are not based on evidence and are essentially a lie designed to manipulate people into eating less.
"This nanny-state agency makes it up as it goes along."
PHE has suggested the same total for both sexes, even though men need significantly more calories, to keep the idea as simple as possible.
In keeping with the new guidelines, Britons will be urged to be cautious at sandwich bars, coffee shops and restaurants, where portion sizes tend to be substantially larger.
While eating out was once considered a treat, busy modern lifestyles have made it more of a habit for many.
Obesity rates for British men and women are the same at 27 per cent – which is the highest of any country in Western Europe.
Yet the Government has been heavily criticised for failing to address the crisis. Its long-awaited obesity strategy last year was branded an 'embarrassment'.
The plan included only voluntary agreements with food manufacturers to cut sugar levels and portion sizes, and there was no mention of controls on advertising. The new calorie guidelines – the One You nutrition campaign – will be rolled out by PHE in March, and adults will be told to remember the '400-600-600' rule.
PHE officials are in talks with coffee shop chains and supermarkets to promote healthy breakfast and lunch options within the limit. But many popular choices fall outside the total.
For example, a large bowl of breakfast granola can contain 500 calories, while a muffin and a latte have 600 calories.
A meal deal lunch of a sandwich, crisps and fizzy drink has 700 calories and an Indian takeaway can contain 1,300 calories.
A PHE spokesman said: "We can no longer hide behind the charade that having a takeaway or eating out is merely a treat. Adults consume 200 to 300 excess calories each day and this calorie creep is contributing to weight gain and other serious health conditions. This is why we're working with high street chains to offer healthier options through our reduction programmes and new One You nutritional campaign."
Officials have deliberately set the guidelines low because they suspect adults will underestimate their calorie intake and will fail to account for calorie-laden drinks including lattes and alcohol.
Many Britons will have over-indulged over the festive period and the average adult eats 5,000 calories on Christmas day alone, double what they need.
Public Health England is particularly worried about obesity rates among the middle-aged as they are at much higher risk of severe illnesses later in life.
Figures show that 71 per cent of adults aged 45 to 54 are overweight or obese, while 25 per cent have high blood pressure and 19 per cent do almost no exercise. They are much more susceptible to diabetes, several types of cancer, heart disease, strokes, liver failure and dementia.
This latest campaign comes two years after the Government introduced new alcohol guidelines to reduce the health risks of excessive drinking. Last March, PHE announced voluntary rules to reduce the size of chocolate bars and other treats by a fifth.