Possible mechanisms and explanations
Both diets were equally satiating, as measured by subjective satiety recorded in parallel with a 4-day weighed food record. Mean satiety for both diets 30 minutes after meal initiation was 1.2 Rating Scale units, which is between “somewhat satisfied” and “satisfied” and is slightly lower than previous results . This probably still indicates adequate satiety, since the ratings are from all meals including snacks, with an average of about five meals per day on both diets, slightly more than in previous studies . In support of this conclusion, five comments from the survey, all relating to the Paleolithic diet, were on being satiated (e.g. “no difficulty becoming full” and “have not been overly hungry at any time”) and only one participant, when on the Paleolithic diet, commented on being hungry (“almost always hungry”).
The Paleolithic diet was more satiating per calorie, despite its lower content of supposedly satiating fiber , which also didn’t correlate with the satiety quotient for energy. This greater satiating capacity may instead have been caused by the lower energy density of the paleolithic diet, as evidenced by the significantly higher satiety quotient for energy density for the Paleolithic diet [9, 10]. Water incorporated into a food increases its satiating capacity by reducing its energy density , and although we found no difference between the diets in calculated water content, there was a significant correlation between water content and satiety quotient for energy density. Differences in beverage intake could also potentially have affected satiety , but we found no such differences between the diets, although there was a correlation between spirits and satiety quotient for glycemic load.
Consistent with our previous results , there was a higher relative intake of protein with the Paleolithic diet (24 ± 3% of dietary energy) compared to the diabetes diet (20 ± 4%9. High-protein diets reportedly reduce appetite and ad libitum caloric intake [13–15]. However, as in our previous study, there was no correlation between relative protein intake and satiety quotients, and no difference in absolute intake of protein between the two diets, making the relative difference in protein intake an unlikely explanation for the difference in satiety.
Just as in our previous study, we found significantly lower carbohydrate intakes in both absolute and relative terms with the Paleolithic diet, a candidate explanation for our observed effect on satiety per calorie , but there was no correlation between satiety quotients and carbohydrate intake. Intakes of sources of carbohydrates with previously reported differences in effects on satiety, such as cereals and fruits, differed between the diets , but also didn’t correlate with differences in satiety quotients. Unlike our previous study , there was no difference in sodium intake between the diets , possibly also indicating no difference in salt intake. Assuming a 1:2.5 weight relationship between intake of sodium and salt (NaCl), the participants’ estimated average daily consumption of salt was 6.3 g on the Paleolithic diet compared to 7.4 g on the diabetes diet. There were some comments on the Paleolithic diet concerning salt (e.g. “miss salt”, “Tasteless without salt” and “You miss salt”), which could indicate less added salt and lower palatability, with effects on satiety . However, since we didn’t measure sodium excretion in urine, a better measure of salt intake, we don’t know whether there was any difference between the diets in terms of salt intake. As mentioned above, the intake of sodium didn’t differ between the diets, nor did comments on palatability. Differences between diets in the intake of vitamin B-6 were correlated with differences in satiety quotients for energy per meal, although the clinical significance of this is unclear.
Among the various comments, there was a trend for noticing improved glucose homeostasis on the Paleolithic diet (e.g. “Blood sugar has stabilized.”, “HbA1c decreased from 6.2 to 5.7”), and significantly more comments on losing weight (e.g. “Only noticed weight loss”, “I have lost weight”, “You lose weight”). The comments probably reflect the participants’ awareness during the study of dietary effects, which they can both notice directly and perceive as important. The comments also reflected differences between the diets in weight loss and glucose homeostasis . There were more comments on the Paleolithic diet being difficult to adhere to (e.g. “The variety has meant that my wallet has taken a hit.”, “I miss bread a lot”, “Somewhat monotonous diet” and “Difficult to adhere to. Miss milk and cereal products”) compared to the diabetes diet (e.g. “can’t do anything spontaneously, must plan”, “However, it can be difficult to get invited out when you can’t just eat anything.”). This is not very surprising, since the Paleolithic diet necessitates greater changes to most people’s diet compared to the diabetes diet. Importantly, the comments on the Paleolithic diet were not overly negative and some were also positive (e.g. “I strongly believe in it and will certainly use much of it in the future.”).