Partner's Presence Cuts the Body's Regulatory Effort by up to 12%

Adults digesting an identical 50-gram carbohydrate meal showed a 14.55% lower cumulative blood sugar response when their romantic partner sat beside them than when they ate alone. That figure, from a study published in Science Advances, anchors a broader finding: the human body runs its basic internal maintenance more cheaply when a close companion is in the room.

The four experiments, led by Monia Masalha and senior author Shir Atzil of The Hebrew University of Jerusalem, tested what the authors call "social physiology" — the idea that a partner's physical presence directly reduces the effort the body spends keeping itself stable.

What did the experiments measure?

Every organism must hold its internal environment within a narrow range — a balancing act biologists call homeostasis. Managing temperature, digestion and nervous system arousal consumes energy. The team quantified that cost by measuring how far a bodily signal strayed from baseline during a challenge and how long it took to return.

The adult experiments drew on 180 healthy volunteers aged 18 to 37, all in monogamous heterosexual relationships of at least nine months, producing 339 paired observations in a living-room-style laboratory where couples could talk or touch freely. Participants completed each challenge alone and with their partner on the same day, in randomized order. The datasets and analysis code were posted publicly on the Open Science Framework.

How large were the effects across systems?

• Blood sugar: In the first experiment, 108 participants (54 couples) fasted overnight, ate 102 grams of white wheat bread, and tracked glucose with finger-stick tests over two hours. Glucose spikes were smaller and subsided faster with a partner present. Between first-session groups, the partner condition showed a 23.9% lower cumulative glucose response.
• Temperature: In 116 adults, skin temperature during five minutes in a 12°C cold room dropped less and rebounded faster together — a 16.17% smaller cumulative drop between groups and 6.76% smaller within individuals, the latter passing only a one-directional test.
• Stress: In 115 adults receiving two mild forearm shocks, cumulative skin-conductance arousal — a measure of fight-or-flight nervous system activity — was 5.98% lower with a partner present between groups; a 1.89% within-person reduction was not statistically significant.

Pooled across all 339 observations, physiological expenditure was 7.59% lower within individuals and 12.07% lower between groups when accompanied. The pattern held after accounting for relationship satisfaction, body mass index, time of day and session order.