Complex sentence: There is limited data on the metabolic effects on humans eating the diet, however a review suggested that a paleolithic diet could be a useful alternative to the unhealthy Western diet, however following the Paleo diet can lead to nutritional deficiencies.
Split into simpler sentences: There is limited data on the metabolic effects on humans eating the diet, though a review suggested that a paleolithic diet could be a useful alternative to the unhealthy Western diet. It has been noted however, that following the Paleo diet can lead to nutritional deficiencies.