Health impacts and dietary composition of Paleolithic and Australian Guide to Healthy Eating Diets in Australia

The Paleolithic diet is promoted in Australia for improved gut health. However, it excludes grains and dairy, food groups that form part of the evidence-based Australian Guide to Healthy Eating (AGHE). While total dietary fibre intake can be maintained from consumption of vegetables, fruit and nuts, it is not known if the elimination of grain-based foods results in changes to resistant starch (RS) intake. The Paleolithic diet can be classified as a low carbohydrate diet, however, interventions examining the impact of low carbohydrate diets on gastrointestinal health have been short-term and very low in dietary fibre, limiting comparison with a Paleolithic dietary pattern. Serum trimethylamine-N-oxide (TMAO) arises mainly from colonic fermentation and hepatic conversion of animal protein and is positively associated with cardiovascular disease, but changes to RS intake may alter concentrations. With available literature on the Paleolithic diet examining only cardiometabolic and anthropometric outcomes, there exists a need to examine both fibre fraction intake and markers of gastrointestinal health, including the composition of the microbiota. The PhD research comprised three separate studies. Studies One and Two re-examined data from a four-week randomised dietary intervention in healthy women (n=39) using the Paleolithic (n=22) and AGHE diets (n=17), to understand fibre fraction intake and to determine whether the short-term dietary change induced changes in serum TMAO concentrations. Study Three comprised a new, cross-sectional study and examined markers for dietary intake, cardiovascular and gastrointestinal health; comparing the results to a control group following a standard Australian diet. Forty-four long-term followers (\u3e1 y) of the Paleolithic diet and 47 healthy controls were recruited; three-day weighed food records, diet history, anthropometric measures, fasting blood, 24-hour urine and 48-hour stool samples were collected. Food group, fibre and RS intake were estimated from weighed food records; serum TMAO concentrations were measured using LC-MS; faecal biochemistry with LC and GC-MS; faecal microbiota composition was analysed using 16s rRNA sequencing of the v4 region. The short-term intervention comprising Studies One and Two showed RS intake postintervention, on a Paleolithic diet was significantly lower (RS Minimum 1.39 ± 0.95 g/day, RS Maximum 6.52 ± 4.59 g/day), than intake in the AGHE group (RS Minimum 2.46 ±2.26 g/day, RS Maximum 9.91 ± 9.06 g/day) and resulted in significant differences between groups (P Study Three showed variation in the level of adherence to the Paleolithic diet and resulted in the stratification of the cohort into Strict Paleolithic (SP) (n=22) and Pseudo-Paleolithic (PP) (n=22) groups. Total dietary fibre intake was similar in the SP and control groups (30 g/day versus 27 g/day) and significantly higher than that of the PP group (21 g/day) (PBifidobacteriaand Roseburia genera, and increased abundance of TMA producing genera Hungatella. Lower RS and carbohydrate intake, combined with high fat intake were associated with changes in microbiota and reduced abundances of beneficial genera in the Paleolithic group. The lack of differences between groups observed in SCFA excretion and the association with vegetable intake is supportive of dietary recommendations to increase consumption and may indicate a mechanism via which vegetables exert beneficial health impacts. The significantly higher concentrations of TMAO in the SP group and the association with both whole grain intake and the microbiota indicates that a variety of carbohydrate sources and fibre components may be required to maintain colonic health. Future research should now focus on including markers of intestinal permeability and inflammation to confirm these findings