A conventional wisdom is that you should never go grocery shopping on an empty stomach. Intuitively, this makes sense: if you’re already full when you go to buy food, you’ll be less tempted to buy extra food items. However, studies on the topic discovered that this is not always the case. Rather, while this is true for people who are not overweight, people who are overweight sometimes buy more food if they eat before shopping.
What the research shows us
Studies show that for most people, eating before going grocery-shopping is a good idea:
- One study found that short-term food deprivation, in terms of not eating for a few hours, leads people to buy more high-calorie products, such as candy and salty snacks.
- Another study found similar results, so that when people are hungry, they are interested in buying more food items compared to when they are full.
However, neither one of these studies differentiated between overweight and normal-weight participants. On the other hand, studies which did examine the shopping patterns of overweight participants compared to participants with a “standard” weight, showed that there is a significant difference between the two groups:
- A study which looked at purchasing behavior in a large supermarket found that people with a standard weight tend to purchase more food when they are hungry, while overweight people tend to purchase less food.
- A different study found similar results, which showed that “normal individuals bought more food if they were deprived than they did if they had recently eaten. Overweight individuals actually bought more food if they had recently eaten than they did if deprived.”
Researchers are not entirely certain what leads to this difference. One suggestion is that for people with a standard weight, increased hunger leads to increased impulse buying, as evident in the fact they purchase more items than they expect to. Conversely, when overweight people eat before grocery shopping, they might become more focused on food, which preemptively increases their intention to buy extra food. This is reflected in the fact that people with a standard weight tend to overshoot their estimated bill when buying food on an empty stomach, while overweight participants tend to decrease both their estimated bill as well as the amount of food they buy in practice.
Disagreements, variations, and what works for you
It’s important to note that there are various discrepancies between different studies on the subject, possibly due to different methodologies (for examples, see this paper, this paper, or this one, all of which found slightly-conflicting results).
It’s also difficult to determine whether the fact that overweight people were hungrier is the reason why they purchased less food. It’s possible that they were more likely to be dieting, which explains both their hunger, as well as their reduced intention to purchase food (although one study did account for this and showed that the effect still appears). In addition, there was also variation in terms of how hungry participants were, and in some cases there was a difference between how low levels of hungers affected people, compared to high levels of hunger.
Overall, this means that we can’t be sure that if you’re overweight then you’re likely to buy more food if you’re full, but it certainly raises the possibility that this might be the case, and that the general notion of “never go grocery shopping on an empty stomach” isn’t necessarily true for everyone.
In addition, it’s important to remember that there is always individual variation. Some people with a normal weight might be motivated similarly to people who are overweight, and vice versa. Furthermore, the definition for ‘overweight’ is also not entirely clear, and can vary according to different sources.
Therefore, the best way to know for sure is to experiment yourself, and see what works better for you. One way to do this is to keep grocery shopping as you normally do, while paying attention to what you buy, and to how hungry you are at the time. It might be immediately obvious that when you’re hungry, you tend to buy tons of snacks. In cases when it is not so obvious, you can keep receipts from your purchases, and write on each one how hungry you were when buying the food.
You can also try to actively alternate between going grocery shopping while hungry and while full, and then compare the amount and type of food that you buy each time. To ensure that your results are accurate, try to minimize the influence of external variables, such as going shopping with other people versus going alone. It’s best to do this a few times in order to reduce the influence of these variables (which are known as confounds), but it’s likely that after one or two times you’ll already have a pretty clear answer.
Overall, it’s easy to point to the findings of just one paper, and popular media loves to simplify things and spread convenient generalizations. As you saw however, the truth is more complicated than that. At the end of the day, the important thing is to be aware of this complexity, and to understand that the most important thing is to find out what works for you.
Summary and conclusions
- People who are not overweight generally tend to make fewer impulse purchases when they go grocery shopping on a full stomach.
- Conversely, people who are overweight tend to actually buy less food if they go grocery shopping when hungry. This has been attributed to a reduction in the amount of food that these participants intend to buy.
- There is variation between different studies, and between the individuals who participated in each study.
- The best solution to finding what works for you, is to experiment and see which type of purchases you make when you’re hungry, and which ones you make when you’re full.