That does not mean however, that their "diet" cannot coincidentally have been healthier than what some people eat today. They surely ate food back then, that was less processed and less unnecessary stuff added to it. Eating whatever you can get your hands on in a less developed time, can mean, that people ate healthier, at least when they had something to eat and did not starve. There does not have to be a nutrition expert around at the time or any intentional process by people to "keep a diet".

Given that their 'diet' resulted in them being chronically malnourished with such lovely diseases as rickets and pellagra I'd take what we have today thanks.

People today seriously underestimate how common famines were.

https://en.wikipedia.org/wiki/List_of_famines?useskin=vector

If you filter by country until the 20th century you had a famine roughly every 5 years.