London: Carlos Sainz is a happy eater again and the Spanish Formula One driver's mother is delighted.

Heavier, faster and more physical, the 2017 cars are subjecting drivers like the Toro Rosso youngster to far greater G-forces through corners that can now be taken flat out on fatter tyres.

As a result, Sainz and others have been putting on muscle over the winter to gain upper body strength. Previously they were more preoccupied with losing weight in a sport where the lightest men have enjoyed an advantage.

Sainz, whose father and namesake was a world rally champion, was vocal last year about the dangers of shedding too much but he said during testing in Barcelona that the situation was now much healthier.

"This year I have had diets, but diets to be fit, not diets to be as slim and as skinny as possible... Because of that, I am a much happier person," said the 21-year-old.

"At the end of 2016 my mum could tell me, every time I was coming home: 'You look like you are not yourself, you look very skinny, you can see your bones here. It's not normal.

"She's extremely happy and she now sees a smile on my face when I eat her food, while before I was sitting there sad with a piece of chicken and I was completely annoyed about it."

A year ago, Sainz and other drivers such as Red Bull's Australian Daniel Ricciardo were being pushed to shed kilos to gain performance.

Formula One cars have a minimum weight limit, minus fuel but with driver included, and designers aim to get it down as far as possible so that additional ballast can be distributed around the car to improve handling.

In 2014, the first year of the V6 turbo hybrid era, the limit did not compensate sufficiently for the heavier engines and drivers had to lose weight - in some cases an unhealthy amount. Now, it is important to be strong enough to get to the finish.

"I think this year they will be proper gladiators out there, you know," commented Mercedes's retired champion Nico Rosberg.