Ready-to-Eat or Ready-to-Heat? Get Ready to Gain

Are you ready to pack on two pounds for the sake of convenience?

Posted Nov 13, 2019

How many of your meals come from a supermarket freezer or are highly prepared and come in boxes? There’s no question that ready-to-eat or other highly processed foods are convenient and save time compared with making meals from scratch. Processed foods also tend to be less expensive and have a longer shelf life. Ready-to-eat or ready-to-heat meals now constitute the majority of calories consumed by Americans. Despite their advantages, you may be concerned because these foods are loaded with sugar, salt, and fat, which can contribute to obesity.

A new study from the National Institutes of Health shows that it’s not just the sugar and fat in processed foods that result in weight gain. Twenty adults were confined to an NIH ward for 28 days. They were given either an unprocessed diet or a highly-processed diet for two weeks. At the end, they switched, so all subjects had two weeks on each diet. They were fed three meals daily and the processed and unprocessed meals were matched for fiber, sugar, sodium, micronutrients and the total number of calories.  

Although there were no differences in the ratings of satisfaction and pleasantness of the meals, the participants who had the processed meals consumed an average of 508 extra calories per day. In two weeks of the processed food diet, they gained two pounds. Most of the extra consumption occurred during breakfast and lunch; dinner consumption was equal. When they switched back to the unprocessed diet, they lost the two pounds.

It’s not clear why the highly processed food resulted in more consumption and weight gain since the participants seemed to like the diets equally. One possible explanation is that they ate processed foods faster. Previous research has shown that faster eating typically results in more eating. Another possibility is the effect of hormones on consumption. A hunger hormone called ghrelin was decreased during the unprocessed diet so participants felt less hungry while PYY, an appetite-suppressing hormone, increased during the unprocessed diet.

You may have noticed that fresh whole foods are more expensive than factory-prepared foods. In the study, the weekly cost of the unprocessed meals was $151 while the highly processed meals cost $106. The researchers wonder if processed foods could be reformulated to reduce their weight-gaining characteristics while retaining their palatability, economy, and convenience. Even if this is possible, reformulated processed foods won’t be on supermarket shelves any time soon so cutting back on processed foods now is a good idea. A little extra effort now (e.g., prepare your lunch in the evening and take it to work) will avoid the weight gain that comes with processed foods.


Hall et al., (2019). Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metabolism 30, 67–77.