PARIS — Even in a country renowned for its exquisite food and adhesion to regular meal times, there has been no escape from “le snacking” and the rise of obesity.

The French are now consuming so much fat, salt, and sugar that — starting Friday — all advertisements for products considered unhealthy will be accompanied by health warnings.

They will accompany publicity in newspapers and magazines, on television and radio, and online.

As fast-food chains like McDonald’s become more and more popular, ministers want people to concentrate on fresh food and vegetables and to increase the amount of exercise they get.

The Health Ministry, which designed the measure, says it will help children “guide themselves” toward making better “eating decisions.”

“We want people — and particularly young people — to cut back on the snacking and get back to healthy habits,” a spokesman said.

Advertisers who refuse to run the messages will be fined 1.5% of the cost of the advertisement, to be paid to the National Institute for Health Education.

They will have a choice of four officious-sounding but simple warnings, which Xavier Bertrand, the health minister, said would be regularly updated to keep them effective.

They include: “For your health, eat at least five fruits and vegetables a day” and “For your health, undertake regular physical activity.”

The advice flies in the face of the image of the svelte and cuisine-conscious French, perpetuated by books like Mireille Guiliano’s bestseller, “French Women Don’t Get Fat.”

The book argues that the French can eat croissants and foie gras without ballooning because they savor flavors and do not eat huge portions.

But growing numbers of processed snacks and ready-made meals with high fat, salt, and sugar content are changing that image.

According to government figures, 5.9 million of France’s 63.4 million people are obese, and 20 million are overweight.