How Food Portions Affect Eating Habits (The Portion Size Effect)

According to WHO, with over 300 million people deemed clinically obese, obesity^[1] has reached epidemic proportions. We are in a ‘weight-watching’ culture where we give careful attention to losing fat and maintaining a healthy weight or muscle mass proportions. One way is paying attention to food portion sizes. Portion size refers to the size or amount of food you’re consuming. Many packaged foods mention the recommended serving size to meet daily nutrition requirements. That isn’t portion size. Portion size is the volume of food you actually consume, regardless of how calorie-rich the food is. Controlling that size is called portion control.

The Portion Size Effect (PSE)

Have you ever mindlessly consumed a jumbo popcorn at the movies or a huge pack of biscuits or chips just because they were set before you? This is usually the case after a big buffet meal or at your grandmother’s house (where she keeps piling on the food). Why is it that we eat more food when we are offered more?

The Portion Size Effect (PSE) occurs when one eats more food when offered more. Experiments demonstrate^[2] that people consume more food when they are served larger portions of food. It does not necessarily depend on the person’s body weight – normal weight & obese people^[3] experience the PSE. This effect can sustain^[4] for several months after exposure to larger quantities of food. It also contributes to excess consumption^[5] of high energy density foods because PSE increases as the food’s energy density increases. A study^[6] showed that participants who saw a smaller portion of food (instead of a larger portion) believed that normal food portions are smaller. They also consumed less of the snack the next day. So the portion size effect – overeating because of getting more food – also has a weaker opposite direction – undereating because of seeing lesser food.

PSE can harm one’s health due to overconsumption and result in excess body weight. How do people fall for this illusory effect? And what can we do to reduce its negative effects?

3 Psychological factors that affect Eating habits

We consume food when we get a basic biological drive of hunger, but we also eat because of biologically unnecessary factors like cognitions, hedonics, a person’s environment, circumstances, and emotions. These factors usually work together, not in isolation.

1. Cognitive factors

Cognitions related to eating refer to knowledge about the government’s diet recommendations, about healthy foods, one’s attitudes towards a healthy lifestyle, personal goals, ability to focus on food satisfaction, etc. Having positive cognitions concerning a healthy lifestyle^[7] results in one implementing healthier routines in daily life. Having more knowledge^[8] about nutrition also creates a tendency to meet daily nutritional intake. Cognitively controlled eating refers to how cognition affects consumption habits. For example, many people avoid certain foods due to religious reasons, or to lose some weight, or because of a certain stance they have (like vegans and vegetarians against animal cruelty). High cognitively controlled eaters are more likely to eat less when offered more, thus less likely to succumb to the portion size effect. 

2. Hedonics & Emotions

Hedonism refers to the pursuit of pleasure and avoidance of pain. Food, through its sensory properties like taste and aroma, provides pleasure and satisfaction to the eater. We prefer & desire certain foods because of their Hedonic properties, and that makes us consume those foods more. Going out for a burger to a particular restaurant (because their burgers are the best) is an example of how hedonics plays a role in the overconsumption of certain foods. 

Bagged a job that you never thought you’d get? Celebrate with delicious food. Going through a break-up? Grab a tub of ice cream. We tend to eat more^[9] because of positive emotions, negative emotions, and stress. However, in some individuals, those emotions can also reduce food intake. The link between hunger and emotions may be deeper than treating oneself. Evidence shows^[10] that craving people when you are lonely and craving food when you are hungry activate the same brain regions (along with a few other different regions). So battling loneliness with food may be a deeply biological coping mechanism.

3. Situational factors

Consumption norms refer to the normal behavior we consider like eating a particular food at a particular time or a typical quantity at a specific place. One study^[11] demonstrated that people prefer ‘breakfast foods’ for breakfast and ‘lunch foods’ for lunch, but that preference doesn’t affect how much they enjoy or consume. The effort for consumption as well as distraction also plays an important role. More the effort to consume, the less likely you are to consume it. People also consume more in restaurants than in cafes, homes, or non-eating spaces. Distraction is related to eating with your family and friends, which results in conversation. When distracted, people tend to eat more. It can also cause an effect wherein the more people we eat with, the more we eat. 

How social norms affect the portion size effect

Social norms convey the right amount to eat, what to eat, and when to eat. For example, eating 4 slices of a large pizza for dinner could be considered normal eating. But eating 1 slice could seem like unusual behavior. People usually eat one portion size, even if they are served more in that one portion. Especially when they serve themselves. A study^[12] saw that when people self-serve ice-cream into a bigger bowl or with a bigger spoon, they serve and consume more. Research suggests^[13] that being served smaller portions alter our belief about the ideal amount of food to eat. It even reduces future consumption because the size influences what we think is the norm for that food.

People also eat more when surrounded by people (especially people they know) who eat a large amount. This was seen in university students^[14] who based their portion size on other students’ portion sizes. Some were told that either a minority and a majority of similar people approved of their portion sizes. Both conditions showed that people ate more from larger portions. But the portion size effect was lesser when it was based on the minority group’s behavior or approval. 

Other cues that affect eating habits and portion sizes

We’ve seen the influence of social norms and psychological dimensions on the portion size effect. Various other cues can also affect the portion size effect and overall eating habits. 

Many environmental, individual, and food-related factors influence the portion size effect, portion control, and eating habits. Here are some highlights from a review of many studies^[15].

1. We often see nutritional labels on packages talking about recommended serving sizes. Unfortunately, research suggests that these labels don’t aid portion size control because of other packaging elements. For example^[16], children and adults are influenced by how food packaging looks. Adults are influenced by a range of visual cues like package size and shape, and less so by informational cues such as labels. Children tend to eat more from packages that exaggerate food portions.
2. The inherent value of food seems more important than the financial damage it does.
3. As we saw in hedonics, orosensory processing has a great influence on food consumption. Larger portions increase one’s bite-size and are related to a faster eating rate, leaving less oral processing time. Reduced processing time when we eat a large portion delays satiety (feeling full and satisfied). 

Awareness about food intake

We do not always experience the portion size effect. Results^[17] of a small study showed that portion size information did not influence satiety/satisfaction ratings or one’s total intake. Participants focused more on their daily nutritional requirements than the quantity of food, thus taking a more objective approach to eating. Mindful eating is one wellness habit that works alongside counting calories to counter the portion size effect.

People may be aware of excess consumption than intended when they eat larger portions. In a study^[18], female participants were asked how much pasta and tomato sauce they would eat for lunch. A smaller or a larger portion of the same food was then provided and participants served themselves a portion into a second bowl of the same size. After eating enough to feel comfortably full, researchers showed them an image of the amount they had served themselves before the meal. Researchers asked them if they perceived consuming more or less than the image, and how much more or less they had eaten.

Among the women who received a large portion and ate more than they intended, a majority of them correctly identified excess eating. Participants then indicated how much more or lesser they had eaten compared to their intended amount. Those who ate more after receiving a larger portion underestimated their intake by 25%. The study suggests people are aware that more intake from a larger portion leads to eating a larger quantity, but they underestimate the actual amount consumed.

The portion size effect in children

The self-regulation theory claims that children have a natural ability to respond to internal cues of hunger and fullness by adjusting their eating patterns accordingly. However, kids between the ages of 3 and 5 may be susceptible^[19] to the portion size effect. Another study validated the occurrence of the portion size effect with cereal amongst children. Imagining the look, taste, smell, feel, and texture^[20] of energy-rich foods like chocolates & waffles can nudge children to choose healthier portion sizes of those foods. This sensory “imagery” can motivate children to select smaller portions of energy-dense foods without reducing the quantity of healthy foods. Enhancing^[21] the taste of vegetables (broccoli) with butter and salt might not affect how much children eat but serving double portions could get children to eat more vegetables.

13 Tips to Control Food Portions & Eat Healthily

Everybody might experience the Portion Size Effect; sometimes daily for a variety of reasons. So how can we counter these cues that we fall for so easily? The portion size is a modifiable and important determinant of how much one eats. Reductions^[22] to a person’s portion size of their main meal can help decrease daily energy intake even when portion sizes seem abnormally small. Here are some tips to have portion control to eat healthier and improve health.

1. If you enjoy high volumes of food, shift to lower calorie-dense^[23] foods so you can manage your energy intake.
2. Use smaller dishes/plates^[24] or dinnerware^[25] like forks & spoons. People tend to fill about 70% of their plate regardless of how large or small the plate is. So reducing plate size helps one consume less without feeling unsatiated.
3. Use your plate as a portion guide. Vegetables must take up half your plate, protein takes up a quarter and carbohydrates take up the rest. Don’t forget to add half a tablespoon of fats to your plate. Proteins and vegetables will ensure you feel satiated for longer.
4. Hands can also act as serving guides^[26]. People typically require a palm-sized serving of protein, a fist-sized portion of salad/pasta/rice, two cup-handed portions of veggies, and one thumb of fats daily.
5. Ask for a smaller alternative when eating out because restaurants notoriously serve larger than necessary portions of food.
6. Drink about 500ml^[27] of water before a meal because it reduces how much food you consume. Pre-meal water can be a simple tool for portion control.
7. Consume soups, light salads, or water-rich substances like fruits before starting a meal^[28]. They are low energy density foods that reduce your overall energy/calorie intake.
8. Sit down to have meals at a designated place with the purpose of eating.
9. Pay attention and be mindfully aware of what, how, when, and where you are eating. Don’t stay distracted while eating, give 100% of your attention to your eating experience. This approach called “mindful eating” is a well-established^[29] way to reduce food intake without losing satisfaction or compromising health.
10. Don’t eat directly from the container or vessel.
11. Don’t fall for the packages. Read nutritional labels and serve yourself accordingly. 
12. Use a food diary or download a calorie counter app to see how much food you eat.
13. Stop when you feel 80% full.

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