Will Smith's family has a gene which makes them ''crave sugar''.

The 51-year-old actor and his family - including wife Jada Pinkett Smith, and their two children Jaden, 21, and Willow, 19, as well as Will's son Trey, 27, from a previous marriage - all tested positive for a particular gene which means they are more likely to ''become overweight and diabetic'' if they gorge on too many sugary snacks.

In a preview clip for the latest episode of Jada's Facebook Watch show 'Red Table Talk', Doctor Mark Hyman tells the family: ''One of the things that we found was you all have genes that make you more likely, if you eat a lot of starch and sugar, to become overweight and diabetic. You also have genes that make you crave sugar, that make you want to snack.''

The news came as a shock to the family, with Willow exclaiming she was swearing off starch-based foods.

But the doctor went on to explain that the gene poses bigger health risks, as their health could be in jeopardy if they don't look after their bodies.

He added: ''That's a big problem because African-Americans are twice as likely to get diabetes, they're four times likely to get kidney failure, they're three-and-a-half times more likely to get amputations from that. So you're all at risk for that.''

The news comes after Will recently revealed he's going on a diet, after his family began calling him ''Pudge Muffin'' when he started gaining weight thanks to his craving for breakfast muffins.

He said: ''So for breakfast, I was having the four or five muffins. You know, 'Aladdin' was successful, so I was like, 'Muffin, muffin, muffin!' Then for lunch, I would have a Moscow mule, I'd have a little vodka. That was pretty much my routine for the 10 days. I'd wake up, eat five muffins and go back to sleep.

''I had gotten up to 225 pounds and it was the most I'd ever weighed in my adult life. I got to 223 on 'Ali' and I got to 225 on the muffin boat.

''Pudge Muffin was cute. But I don't want to be a Pudge Muffin to my family.''

Hitting his heaviest weight prompted Will to go on a 10 day fast, but that turned out to be dangerous too because his lack of energy paired with his blood pressure medication made him pass out.

He said: ''So I'm going to fast for 10 days. I did it and I got to about four days and I'm [mimes passing out] because I was still taking my blood pressure medicine. So I started taking my blood pressure medicine and my blood pressure was almost way dangerously low.''

Will stopped taking his medication for the rest of his fast and saw his blood pressure even out, and he now believes his high blood pressure was simply caused by his poor diet, rather than an underlying health issue.

He added: ''I couldn't believe I got to 50 years old without knowing you literally are what you eat. I eat food like an addict. I love food, but I realised my relationship with food was I eat for fun. I eat for joy.''