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Why We Underestimate What We Eat

Most of us “cheat” when it comes to admitting what we eat.

Key points

  • Most people underreport how much they eat and underestimate calorie intake by 20 to 50 percent, making it harder to maintain a healthy weight.
  • Dysfunction in a brain region known as the hippocampus can lead to deficits in recall regarding food consumed and feelings of fullness.
  • The Western diet, which is high in processed foods, can also have cognitive effects that result in a reduced ability limit food intake.
AndreyPopov / iStock
Source: AndreyPopov / iStock

Studies show again and again that we humans have a great tendency to underestimate what we have eaten during the day and tend to minimize the calories in the foods that we eat.

Often individuals seeking to lose weight are asked to keep a food diary before they even start. While some people find that recording their intake is a good way to increase awareness of food consumed, others tend to feel embarrassed or guilty about recording everything they eat and so will underreport specific foods or amounts (e.g., number of cookies or chips). Others say that recording food intake is simply too much effort, especially if it requires weighing and measuring foods. Still others have difficulty knowing what a standard serving size is.

There are many studies that utilize dietary recall. Many contain inaccuracies and probable sugar-coating of actual consumption. Indeed, it seems that most of us underestimate our intake. According to a study at Cornell University, everyone does it. Normal weight people underestimate calorie intake by about 20 percent, and overweight people underestimate by about 40 percent. Other sources say it’s more like 50 percent.

Shedding More Light on the Problem

Aside from embarrassment, inconvenience, and sugar-coating, what else could be going on? The answer to that sheds a great deal of light on the problem of underreporting and the larger question of overeating.

A recent article in Frontiers in Psychology (2019) points to deficits in a critical area of the brain responsible for learning, memory, and cognition: the hippocampus. The article is an extensive review that indicates that dysfunction in the hippocampus can lead to deficits in recall regarding food consumed, the sensory experience involved, and feelings of fullness or satiety.

Just as concerning is that hippocampus dysfunction can “weaken our ability to anticipate the consequences of eating, and disrupt memory mechanisms that help us inhibit the tendency to eat.” Taking this a step further, memory dysfunction may mean that a person does not use memories to realize that eating past satiety will not be rewarding. All these consequences are extremely detrimental to the maintenance of normal, healthy weight.

There are several factors that can lead to memory problems when it comes to food consumption, including distraction while eating, or food experiences that may be linked to certain situations (family dinners, watching TV after dinner). The article in Frontiers of Psychology, however, focuses mainly on the effect of the Western diet on cognition, especially as it relates to the hippocampus.

The Western Diet and the Hippocampus Connection

The Western diet is characterized by a high intake of saturated fats and refined carbohydrates, including frequent consumption of processed foods. These foods are manufactured to be high in sugar, fat, and salt and to be highly palatable and rewarding. Unfortunately, it is estimated that 50 percent of the calories consumed by Americans are now from processed items. Statistics also indicate that only 15 percent of Americans are consuming the recommended minimum of five servings of fruits or vegetables daily.

We know that the Western diet is strongly linked to the obesogenic environment that surrounds us. Other factors contribute by encouraging lower levels of physical activity. These factors have been found to co-occur with weakened episodic memory, regardless of age.

What Happens When Our Food Memory Fails

How does this play out in our everyday lives as we make food choices that may contribute to difficulties controlling weight? In broad terms, studies regarding hippocampus dysfunction and those regarding cognitive effects of the Western diet show similar effects on food consumption. That is, there is an increase in food intake, body weight, heightened response to food cues, impaired attention to internal cues regarding satiety, and reduced ability to inhibit food intake.

Little wonder that our Western diet ends up sabotaging our best efforts at attempting to maintain a reasonable weight. Once body fat has accumulated, other perturbations in our physiology make it even more difficult to regulate our energy intake. Excess body fat throws off a wide range of metabolic and cognitive processes.

As a quick example, food consumption causes an increase in insulin production that then reaches the brain. The brain then signals us to decrease food intake. A consequence of overweight and obesity is insulin resistance. Insulin resistance is associated with a dysfunctional hippocampus, which plays out a deficit in episodic memory. That can lead to all the consequences mentioned above: increase in food intake and body weight, heightened response to food cues, impaired attention to internal cues regarding satiety, and reduced ability to inhibit food intake.

What Is the Solution?

The most powerful solution to this problem would of course be to switch from the typical Western diet to a style of eating that embraces whole unprocessed foods, rich in a variety of fruits and vegetables, whole grains, legumes, and lean protein. When we are surrounded by many very appealing manufactured foods, that can be a tough sell. Indeed, many people feel that the Western diet is “normal,” and do not feel that “healthy” foods taste very good.

Alternatively, mindfulness is often used as a means of helping people pay more attention to sensations, memories, thought patterns, and emotions related to what they are eating. Likewise, awareness and attention can be invoked by using a food diary. Both methods, if done honestly, can be a way to jog memory of what has been eaten, take away distraction so that there is more focus on actual intake, and hopefully give an individual the time and space to consider the negative consequences of a food choice or portion.

Looking at the problem even more broadly, disseminating basic information about what happens to our brains and bodies on the Western diet may be extremely helpful. Awareness of the barriers to weight loss brought on by the Western diet may help individuals develop objectivity and more enlightened strategies in the development of a healthier way of eating.


Davidson, T.L., Jones, S., Roy, M., and Stevenson, R.J. (2019). The Cognitive Control of Eating and Body Weight: It’s More Than What You “Think”. Frontiers in Psychology. 10:62.

Klesges, R.C., Eck, L.H., and Ray, J.W. (1995). Who underreports dietary intake in a dietary recall? Evidence from the Second National Health and Nutrition Examination Survey. Journal of Consulting and Clinical Psychology, 63(3), 438-444.

Lang, S.S. (2006). It’s the size of the meal, not the size of the person, that determines how people underestimate calories, Cornell study finds. Cornell Chronicle.

Macdiarmid, J.I. and Blundell, J.E. (1997). Dietary under-reporting: what people say about recording their food intake. European Journal of Clinical Nutrition, 51, 199-200.

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