# Photoplethysmography

An Apple team aligned wrist photoplethysmography (PPG, a green-light measure of microvascular blood-volume change) with meal descriptions to train the Nutrition PPG Language Model (NPLM) and test whether passively collected pulse waveforms carry dietary information. On 1,122,834 meal descriptions from 19,340 participants, near-meal PPG raised the likelihood of the correct meal text to a win rate of 0.69, against 0.60 for a control that kept the same participant and time of day but broke the meal pairing, and 0.50 for across-subject shuffling. Without retraining, the signal raised postprandial satiety prediction AUC from 0.64 to 0.71 in an independent cohort, which the authors frame as augmenting text-based logging rather than replacing it.

An Apple team aligned wrist photoplethysmography (PPG, a green-light measure of microvascular blood-volume change) with meal descriptions to train the Nutrition PPG Language Model (NPLM) and test whether passively collected pulse waveforms carry dietary information. On 1,122,834 meal descriptions from 19,340 participants, near-meal PPG raised the likelihood of the correct meal text to a win rate of 0.69, against 0.60 for a control that kept the same participant and time of day but broke the meal pairing, and 0.50 for across-subject shuffling. Without retraining, the signal raised postprandial satiety prediction AUC from 0.64 to 0.71 in an independent cohort, which the authors frame as augmenting text-based logging rather than replacing it.

An open benchmark evaluates five public PPG foundation models across nine datasets, 26 tasks and four downstream adaptation regimes under one protocol, finding that 35.3% of 68 task-regime combinations show no meaningful gain over a random or constant baseline and 83.8% show no PPG-specific model beating both classical pulse-rate-variability features and a generic time-series foundation model.

An open benchmark evaluates five public PPG foundation models across nine datasets, 26 tasks and four downstream adaptation regimes under one protocol, finding that 35.3% of 68 task-regime combinations show no meaningful gain over a random or constant baseline and 83.8% show no PPG-specific model beating both classical pulse-rate-variability features and a generic time-series foundation model.