Understanding the right portion size for you is necessary for maintaining a healthy weight and a key ingredient to any successful weight-loss program. The simple truth is that many a good weight loss attempt has been undermined by our tendency to add “just a teensy bit more” if something looks good, believing that it either doesn’t matter or that we can somehow make up the difference elsewhere.
Irrespective of the type of diet you are on, identifying the correct portion size allows you to know exactly how many calories, carbs, sodium, or fats you are consuming. It is the cornerstone to building good eating habits, increasing your chances of not only losing weight but keeping it off.
Portion Size vs. Serving Size
Many of the problems related to portion size stem from misconceptions about what the term actually means. For example, if you use the Nutrition Facts label on a food product to direct your portion size, you may already be setting yourself up for error.
What you’ll find on the label is the serving size, a standard set by the U.S. Food and Drug Administration (FDA) to describe “the amount of food customarily consumed in one sitting for that food.” It is simply used as a reference point to describe the amount of food in relation to the nutritional information shown.
The calculation is based on your age, sex, height, current weight, activity level, weight loss goal, and intended weight loss date.
Portion size is different. This is the amount of a specific food that you actually eat and can often be larger or smaller than the serving size on the nutrition label.
Let’s say, for example, that you regularly snack on low-calorie microwave popcorn. A serving size according to the Nutrition Facts label is 3 cups. There are two servings in each full-size bag. If you eat the whole bag, your portion size is 8 cups—double the serving size and double the nutrition values.
Similarly, the recommended serving size of grapes is 1 cup or roughly 16 grapes. Unless you count out the grapes, this “low-calorie” food can increase your carb intake well beyond your intended daily limit.
If you confuse serving size with portion size, your calorie counts will likely be way off and may undermine your weight loss goals.
This is true even with respect to certain diet apps that base their calculations on FDA serving sizes. Unless you have the reference values and make the appropriate adjustments—inputting eight grapes as a half-portion or 20 grapes as a 1.25-portion—the app will be of little benefit to your weight loss strategy.
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Calculating Portion Sizes
There is no right or wrong amount of specific food to eat when you want to lose weight. The proper portion sizes of food are the portions that allow you to fuel your body with energy and nutrients and feel satisfied. However, the ultimate aim of any weight loss plan is to consume fewer calories than your body utilizes to remain at your current weight. You need to do so without depriving yourself of important nutrients, including healthy fats and carbohydrates.
Unlike serving size, the portion size is calculated based on how many calories you plan to consume in a day. You would then plan your menus by calculating how much of a certain food you can eat to remain within that limit.
As such, portion sizes can vary as long as nutritional needs are met. These goals are outlined in the 2015 to 2020 Dietary Guidelines for Americans issued by the U.S. Department of Health and Human Services.2
To determine your correct portion sizes, use a weight loss calculator to determine how many calories you need to consume daily to lose weight. The calculation is based on your age, sex, height, current weight, activity level, weight loss goal, and intended weight loss date.