No, this is not a commercial for Government Employees Insurance Company (GEICO). It's the argument for paleo nutrition and it goes something like this.
Humankind has evolved over the last 2.5 million years, and during that time, humans were mostly carnivores. In other words, our caveman ancestors where hunters and gatherers who mostly ate meat and whatever high fiber sources of plant food they could find. It wasn't until about 10,000 years ago that agriculture was started and plant food was used as a primary source of food, or in other words, less than one half of one percent of our existence here on earth. Hence, humans simply have not had time to adapt to a plant based diet. Even worse, sugar has only really been a big part of our diet for about 100 years, or less than 4/1000's of a percent of our existence. They point to populations that have survived into the 20th century on a "paleo diet," such as the Inuits of Alaska who survived almost exclusively on fish and whale blubber for most of their existence, and who did not have the problems associated with the western diet. However, once flour and sugar was added to their diets, the rates of diabetes, obesity, etc., skyrocketed.
A somewhat more religious version of this argument is that humans have only existed for about 6,000 years and God gave man wheat as the staff of life. However, sugar was never included in the bargain. Humans have only been eating large amounts of sugar for about the last 100 years (or less than 2% of our time here on earth) and our bodies have simply not had time to adapt to the onslaught of sugar we eat. Had we eaten the way God intended us to eat, we would not have problems with obesity, diabetes, high blood pressure, heart disease, and all of the other problems that lead to metabolic syndrome or other problems associated with a modern, western diet (e.g., dental problems). In other words, had we followed the Word of Wisdom as we should have, we wouldn't, as a society, be in this mess now.
I find both of these arguments compelling. Think about what people at the time of Joseph Smith ate. Grains and only a very little meat, but hardly any sugar. The fruit they consumed was in season and in small quantities, and it wasn't bred, as it is now, for sweetness. In short, it was a very healthy way of eating. Our modern diet, high in processed foods and refined carbohydrates, and loaded with sugars, is killing us.