Almonds raised some flu-vaccine antibody readings — but 93% versus 95% is the result that keeps the claim grounded

Can a whole food change how the immune system answers a vaccine? A randomized trial published in The American Journal of Clinical Nutrition on 26 October tested that question in 90 healthy adults aged 40 to 64. For eight weeks, participants ate either 56 grams of almonds a day or 86 grams of pretzels chosen to provide the same energy. Everyone received a seasonal influenza vaccine halfway through the intervention.

The pre-specified primary outcome was seroconversion to at least one influenza strain by week eight. That happened in 38 of 41 people analysed in the almond group, or 93%, and 37 of 39 in the pretzel group, or 95%. There was no statistically significant difference (p = 1.000), and neither strain-specific seroconversion nor seroprotection differed between groups. In plain language, almost everyone mounted the trial's defined response, whichever snack they ate.

A more detailed antibody measurement produced a different-looking signal. For the A/Wisconsin/67/2022 H1N1 strain, the geometric mean antibody titre was 359 in the almond group and 110 in the control group. The geometric mean fold-change from before vaccination was 18 versus 4 for that H1N1 strain and 10 versus 5 for B/Yamagata. These laboratory differences are interesting, but they did not translate into more people crossing the study's seroconversion or seroprotection thresholds.

The investigators also found a higher absolute abundance of the gut bacterium Roseburia hominis after almonds, while short-chain fatty acids and stool consistency did not differ. The study was not a demonstration that almonds prevent influenza, shorten illness or make vaccination unnecessary. It measured immune markers four weeks after vaccination in healthy middle-aged adults, not infections during a flu season.

There are reasons to keep the finding in proportion. Only 90 people were randomized, the main response rate was already above 90% in both groups, and the trial compared almonds with pretzels rather than with no snack. It also cannot tell us whether another nut, a smaller portion or a longer period would give the same laboratory result. Several researchers reported funding from the Almond Board of California, including the lead author's doctoral studentship; that does not invalidate randomization, but it belongs in the interpretation.

For everyday eating, 56 grams is roughly two standard 28-gram servings and supplies substantial energy. Almonds can be a useful source of unsaturated fat, fibre and protein, but this trial is not a reason to add that portion on top of an otherwise complete diet or to treat food as a vaccine booster. The grounded conclusion is narrower: almonds altered some post-vaccination antibody measurements, while the trial's main yes-or-no immune-response outcome stayed essentially the same.