What Are Portion Sizes & Do They Matter?

Most of the time, it's best to let your hunger and fullness cues be your guide.

an illustration of a food scale and measuring spoons
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If you've ever flipped over a package of food, you've probably seen the term "serving size" on the label and wondered if that's the amount you're supposed to eat. You may also often hear the term "portion size." What is the difference between a serving and a portion? And how much are you supposed to eat anyway?

The truth is, there's no hard-and-fast rule on how much you're supposed to eat at once. (Sometimes you're hungrier, and other times you might be less hungry!) Eating an exact serving size is also impractical, as most people don't go around meticulously weighing, measuring or counting their food. Referring to serving sizes may be a helpful guide when managing certain health conditions or working toward a specific health goal. However, the average person doesn't need to whip out the kitchen scale or measuring cup to decide how much to eat.

Portion vs. Serving Size

It may be a surprise to some people that there's no specific amount in a portion. A portion is simply the amount you choose to eat at one time, such as for a meal or a snack. It's entirely up to you to decide!

However, a standard portion size, also known as a serving size, does have a specific measure. Unlike a portion, a serving size uses a standard measurement that would be appropriate for the type of food, such as a cup, tablespoon, slice or pieces. Each type of food will have its own serving size, and the Nutrition Facts label will give you information about the food based on that serving size.

While serving sizes have appeared on food labels since the 1990s, it was only recently (the first update in 20 years) that the Food and Drug Administration required the serving size to be updated to align with people's actual eating habits. This means that, by law, a food's serving size must reflect the amount people typically eat in one sitting.

Sometimes the portion and serving size are the same, but often they are not. Remember that portion sizes may change from sitting to sitting while serving sizes do not, as they are a standardized measure. It's important to note that a serving size, while it may reflect what people commonly eat in one sitting, is not a recommendation of how much you should be eating at one sitting.

Servings for a Healthy Dietary Pattern

The departments of Agriculture and Health and Human Services release the Dietary Guidelines for Americans every five years. The DGA offers recommendations for a healthy diet or dietary patten, the foods and beverages a person eats or drinks over time.

Currently, the recommended servings for a healthy dietary pattern are based on a 2,000-calorie diet for an average American. The daily amount recommendations are:

  • Vegetables (starchy and nonstarchy vegetables, beans, peas, lentils): 2½ cups
  • Fruits: 2 cups
  • Grains (whole and refined grains): 6 ounce-equivalents
  • Dairy: 3 cups
  • Protein (seafood, meat, poultry, eggs, nuts, seeds, soy products): 5½ ounce-equivalents
  • Oils: 27 grams

This information serves as a guide but may vary depending on individual health conditions or disease, cultural food preferences and activity level.

Do Portion Sizes Matter?

For most people, measuring out their food as a way to decide how much to eat isn't necessary. Equally unnecessary is limiting how much you eat to follow the standard serving size that is listed on packaged foods. That said, following more standard portion sizes may be useful when someone needs help meeting their nutritional needs or is working toward a specific health goal. Here are some pros and cons of paying attention to portion sizes.

Benefits of Using Portion Sizes

Portions can be helpful or even necessary in some cases, including:

Athletes or People Training for an Athletic Event

Athletes, bodybuilders or people training for rigorous athletic feats may have specific nutritional needs. Nutrition can help with their performance, and athletes need to get enough calories, carbohydrates, fluids, iron, vitamins, minerals and protein. The type of sport and amount of training will impact how much food they need. For these individuals, tracking their portion sizes can become a helpful way to ensure they stay nourished, hydrated and healthy.

Malnourished Individuals

Someone who is malnourished due to illness or food deprivation may have specific instructions on how to introduce more food and get back to health.

Someone with an Eating Disorder

Eating disorders are serious illnesses that lead to disturbances in a person's eating behavior. Individuals with an eating disorder may have a distorted view of food and/or their body image. During treatment, as they work with their medical team, they may have specific goals around what they eat and how much they eat.

"Individuals in eating disorders and disordered eating recovery benefit from being mindful of adding enough carbs, fat and protein to their plate. While measuring isn't helpful because it can become too rigid, being aware of having enough can be helpful to be sure the body is getting enough energy that it needs from food," says Katherine Metzelaar, M.S.N., RDN, CD, a registered dietitian based in Seattle.

Medical Conditions That Require Restrictions of Certain Foods

Some medical conditions will require limitations on portion sizes. For example, a person with diabetes needs to be mindful of which type and how much carbohydrates they eat in a sitting. Someone who has undergone bariatric surgery will have to adjust what they eat and their portion sizes due to changes in their stomach size or how their digestive system processes food.

Downsides of Using Portion Sizes

In general, people don't eat the exact same amount at each sitting, nor does doing so provide any benefits. Adhering rigidly to portion sizes may have negative impacts, such as:

Overreliance on External Cues

Metzelaar notes, "There are many disadvantages of measuring out your food, namely that it disconnects you from your own intuition. Your hunger and food needs change on a daily basis." Rather than eating when you are hungry and stopping when you are full, relying on portions or serving sizes to guide how much to eat can leave you feeling dissatisfied with your meal or snack.

Unhealthy Relationship with Food

Constantly measuring your food can make you become overly preoccupied with what and how much you're eating. Metzelaar adds, "It can lead to disordered eating behaviors. It also can lead to lots of shame and guilt when you don't follow the recommended portion and/or serving size. Additionally, your hunger and food needs change on a daily basis."

Disruption of Your Life

While some people find it helpful to measure their food in advance, such as with meal prep, but most people don't prepare every meal at home. Most of us don't carry around measuring cups or spoons, so if you are measuring everything you eat, it could become very disruptive to your life.

How to Use Portion Sizes in a Healthier Way

Increasing your awareness of portion sizes can give you information about your overall diet and energy needs.

For example, you may notice that you're feeling sluggish and low-energy throughout the day. This may be an indication that your portion size is too small and that you may need to increase your portion size to meet your energy needs. You may notice that your portions are making you feel overly full and uncomfortable after your meal. This could be an indication that your portion size was too large. Increasing your overall awareness of how much you eat and how it makes you feel can help you tune into your internal hunger and fullness cues.

Portion sizes can help you meet your nutritional needs for a healthy dietary pattern. If you're noticing that you haven't had any fruits or vegetables in a few days, having a goal to increase your servings of fruits or vegetables over the next few days or weeks can be a healthy and mindful way of using portions.

For people with specific health conditions like malnutrition, diabetes, post-bariatric surgery or an eating disorder, portion sizes may be an important aspect of their recovery. Working with a health care provider or registered dietitian can help you determine how to craft a healthy eating pattern that works for you.

The Bottom Line

Portion size is defined as the amount people eat at one sitting. For most people, portion sizes vary from meal to meal, day to day, or week to week. Serving size (or standard portion size) is determined by the FDA for each food and is based on the amount of that food a person would typically eat in a sitting. It is not the amount that is necessarily ideal for you and does not give you all the information about what you should be eating for a healthy diet.

Understanding portions and servings may be helpful for people with specific needs, such as if you are training for an athletic event or battling illness, which requires more energy and protein. However, for most people, being preoccupied with portions can lead to an unhealthy relationship with food and eating. Having some awareness can help you determine if you are meeting your nutritional needs and goals; however, there's no need to walk around with measuring cups and spoons in your pocket. Ultimately, you control what a portion size is. Don't let it control you.

Up Next: How to Break Up with Diet Culture (and Still Feel Your Best)

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