An epigenetic clock estimates how old someone's body looks biologically by reading chemical tags on the DNA rather than counting birthdays. The versions used here are expressed either as the gap in years between that estimate and actual age, so a positive number means looking older than you are, or as a pace of ageing scaled so that one is the population average rate per calendar year.
Drawn from background physiology, not from this paper.
The authors write that the extent to which adherence to various healthy dietary patterns overlaps, and whether they affect health outcomes through similar or distinct molecular mechanisms, has not been explicitly examined, and that whether diet induced methylation changes converge on distinct biological pathways remains unclear.
Drawn from the paper's introduction.
Ten diet quality scores were calculated for every participant in the Rhineland Study, then recalculated in EPIC-Potsdam as an independent replication. The scores agreed far less than their shared purpose would suggest. Of 6,470 adults, 18 sat in the top quarter of adherence on all ten scores at once, and 77 managed it on at least nine. Meanwhile 1,212 people made the top quarter on at least one score, so the label of good eater attaches to roughly one person in five or to almost nobody depending entirely on which instrument is picked up.
Correlations between the scores ran from 0.61 at the closest, between the unhealthy plant based index and the dietary inflammatory index, down to 0.18 between the Nordic diet score and EAT-Lancet.
Against the biological ageing measures the picture inverted. All ten scores were significantly associated with the pace of ageing measure after false discovery rate correction, in the expected direction, though the sizes differed. DASH moved the pace of ageing by minus 0.10 SD per standard deviation of the score (95 percent CI minus 0.12 to minus 0.08) and the Nordic score by minus 0.07 SD (95 percent CI minus 0.09 to minus 0.05), while the dietary inflammatory index ran the other way at plus 0.07 SD (95 percent CI 0.05 to 0.08). EAT-Lancet was the exception on the clock measures, showing no association with either age acceleration measure and producing no epigenome wide significant site in either cohort.
Across nine patterns, 240 methylation sites reached epigenome wide significance, from 54 for AHEI-2010 down to 3 for the unhealthy plant based index, and 39 of those replicated. The specific sites and genes barely overlapped between scores. The pathways they belonged to did.
| People in the top 25 percent on all ten scores at once | 18 of 6,470 |
| People in the top 25 percent on at least nine of ten | 77 |
| People in the top 25 percent on at least one score | 1,212 |
| DASH, pace of ageing, per 1 SD (4.4 points) | minus 0.10 SD (95% CI minus 0.12 to minus 0.08) |
| Nordic, pace of ageing, per 1 SD (3.4 points) | minus 0.07 SD (95% CI minus 0.09 to minus 0.05) |
| Dietary inflammatory index, pace of ageing, per 1 SD (1.7 units) | plus 0.07 SD (95% CI 0.05 to 0.08) |
| Scores associated with pace of ageing after FDR correction | all 10 |
| EAT-Lancet score against either age acceleration measure | no association, and no epigenome wide significant site in either cohort |
| Epigenome wide significant sites across nine patterns | 240, from 54 (AHEI-2010) to 3 (unhealthy plant based index); 39 replicated |
| Correlation between scores, highest and lowest | 0.61 (unhealthy plant based vs inflammatory index); 0.18 (Nordic vs EAT-Lancet) |
Proposed by the authors This is the explanation the authors offer in their discussion. This study did not test it.
The authors describe a convergent pathway model. They found minimal overlap in the specific sites or genes associated with different diet quality scores, yet substantial overlap in the biological pathways those sites belonged to, so that different healthy diets may influence distinct sets of epigenetic markers while converging on similar processes involving cell signaling, metabolism and neurogenesis.
They note pattern specific arms within that convergence, with the DASH diet showing changes in heart function related pathways and the MIND diet in central nervous system and cognition related pathways.
They leave the transcriptional link open. The majority of identified sites did not show expression associations in blood, which they write does not preclude biological relevance, since blood methylation may serve as a biomarker of systemic dietary exposures whose functional consequences occur in tissues such as adipose, liver or the gastrointestinal tract.
Drawn from Discussion, PMC13526023.
The ten competing definitions of a good diet identify almost entirely different people as good eaters, which means the choice of score is doing a lot of the work in any study that uses one, and yet the molecular signatures they leave behind land in overlapping territory.
Adults of European ancestry in two German cohorts, aged 30 to 95 in the discovery sample.
It undercuts reading any single diet score as the measure of diet quality, and it argues that results attached to one score should not be quoted as if they were about healthy eating in general.
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