"If you are looking for a simple way to better understand Paleo concepts, Darryl's Paleo from A to Z guide is the go-to resource."
-Mark Sisson, best-selling author of The Primal Blueprint and publisher of Mark's Daily Apple
Researchers have found that our ancestors were lean, fit, in good health, and not plagued with modern lifestyle diseases such as cancer, diabetes, and heart disease. Life expectancy was usually as good as if not better than the present day - as long as the risk factors of being eaten by predators, suffering from poor hygiene, contracting a life-threatening infection at childbirth are taken into account.
There are a few studies that support this modern take on the Paleo diet. One study that was widely reported in the British Press in 2008, was the trial run by the Karolinska Institute in Sweden. Published in the European Journal of Clinical Nutrition.
Subjects were only allowed to eat fruit, vegetables, lean meat, fish, and nuts. All beans, grains (wheat, rice), alcohol, sugar and juices were banned. In just 3 weeks the subjects had lost an average of 5 pounds (2.3kg), waist circumference had reduced by 0.2 inches (0.5cm), a 5 per cent decrease in lower blood pressure and had 72 per cent lower levels of a blood clotting agent that could cause heart attacks and strokes.
Dr Per Wandell noted at the time, “Short-term intervention with a paleolithic diet in healthy volunteers showed some favourable effects on cardiovascular risk factors.”
Some other research looking at the impact on health when following a Paleo diet concludes: "Even short-term consumption of a paleolithic type diet improves BP and glucose tolerance, decreases insulin secretion, increases insulin sensitivity and improves lipid profiles without weight loss in healthy sedentary humans."
and also "Even short-term consumption of a Paleolithic-type diet improved glucose control and lipid profiles in people with type 2 diabetes compared with a conventional diet containing moderate salt intake, low-fat dairy, whole grains and legumes."
 Cordain L, Eaton SB, Sebastian A, Mann N, Lindeberg S, Watkins BA, et al. "Origins and evolution of the Western diet: health implications for the 21st century." Am J Clin Nutr. 2005
 Österdahl M, Kocturk T, Koochek A, Wändell PE. "Effects of a short-term intervention with a paleolithic diet in healthy volunteers." Eur J of Clin Nutr. 2008
 Masharani U, Sherchan P, Schloetter M, Stratford S, Xiao A, Sebastian A, Nolte Kennedy M, Frassetto L. "Metabolic and physiologic effects from consuming a hunter-gatherer (Paleolithic)-type diet in type 2 diabetes." Eur J Clin Nutr. 2015