Most consumer research still treats behaviour as something that happens at the level of the individual. We ask people what they buy, what they intend to do, and how they feel about brands.

But if you look at how most of us actually live, that methodology is slightly off. Very little everyday behaviour happens in isolation as many of us share homes, fridges, cupboards, streaming accounts, shopping lists, routines and more. And so what one person does almost always affects at least one other.

In practice, a lot of consumer behaviour is not really individual at all; it’s social and domestic, shaped by who we live with, the routines we share, and the practical realities of being part of a household.

GLP-1s as a very visible example

The recent rise of GLP-1 drugs like Ozempic and Wegovy has made this dynamic much easier to spot. When one person in a household starts taking a drug that reduces appetite and interest in food and alcohol, the effects are rarely contained to that one person. Grocery shops change, shared meals get smaller, snacking habits change and takeaways happen less often.

There’s already data to back this up; analysis of U.S. consumption data suggests that when a household member starts using a GLP-1 drug, total household grocery spending falls by around 5% within six months, with sharper drops in categories like snacks and processed foods. Other studies put the drop closer to 6–11%, and also point to reduced spend in restaurants and fast food.

What’s interesting is not just the size of the effect, but why it happens. It’s not that everyone in the household suddenly becomes health conscious, but simply that behaviour is shared. When you tend to shop together, cook together and eat together, one person’s changed appetite can change the whole system.

This happens all the time, we just don’t label it

GLP-1s are just the most obvious current example of this but there are many examples where behaviour from one person can impact the whole house, such as:

• One partner giving up drinking: alcohol intake across the household usually drops
• One person going vegetarian: meat consumption often falls for everyone
• One parent getting into budgeting: brands and products start changing across the trolley
• One person developing an intolerance or allergy: entire food routines change
• One person getting really into health and fitness: portion sizes shrink

We tend to think of these as individual choices, but in reality, they end up being collective adjustments as these decisions cross over into shared habits, shared shopping and shared norms.

Why this matters commercially

From a brand perspective this has a slightly tricky implication, as we need to acknowledge that one behavioural change rarely equals one consumer. In categories that are shared or habitual, such as food, drink, streaming, eating out, etc., one person changing their behaviour can mean a 3 or 4 person shift in demand.

This is particularly relevant for:

• food and drink brands
• restaurants and hospitality
• subscription services
• anything with a main decision-maker or “gatekeeper”

Brands in these spaces often underestimate secondary effects. They see behavioural changes as one person dieting, quitting alcohol or using GLP-1s. However, what they’re really observing is the start of a household-level shift.

The research blind spot

The reality is that most consumer research still measures the wrong unit. We tend to ask questions such as:

• How often do you snack?
• How much do you drink?
• What influences your purchase decisions?

But we rarely ask ones like:

• Whose preferences dominate shared decisions?
• Has anyone else in your household changed their behaviour recently?

What we end up with is very clean individual data, yet a very incomplete picture of how behaviour actually works.

A more useful way to think about consumers

A more useful way to look at this is not in terms of individual consumers, but in terms of how households actually function. Influence is rarely evenly distributed as someone usually shapes what gets bought, what gets avoided and what feels “normal”. And when that person’s behaviour changes, shared decisions change with it.

The important questions for brands are simple ones: who tends to influence others within the household, who controls shared decisions, and whose behaviour sets the baseline that everyone else adapts to?

GLP-1s have made this easier to see, however the same dynamics have always existed, they were just much easier to overlook.

If you’re interested in undertaking this type of research in your sector, get in touch today to book an initial scoping call.