Food Variety, Calorie Intake, and Weight Gain

Let's kick off this post with a quote from a 2001 review paper (1):

Increased variety in the food supply may contribute to the development and maintenance of obesity.  Thirty-nine studies examining dietary variety, energy intake, and body composition are reviewed. Animal and human studies show that food consumption increases when there is more variety in a meal or diet and that greater dietary variety is associated with increased body weight and fat.

This may seem counterintuitive, since variety in the diet is generally seen as a good thing.  In some ways, it is a good thing, however in this post we'll see that it can have a downside.

When doing my usual rounds of the literature last week, I came across a fascinating paper I hadn't seen before titled "Variety in the Diet Enhances Intake in a Meal and Contributes to the Development of Obesity in the Rat", by Dr. Barbara Rolls and colleagues (2).  As the title suggests, they examined the effect of food palatability and variety on food intake and fat gain in rats.  They tested six different diets:

1. Regular rat chow
2. Rat chow plus crackers
3. Rat chow plus cookies
4. Rat chow plus chocolate
5. Rat chow plus crackers, cookies, or chocolate, with each of the palatable foods given in succession (i.e. chow plus crackers, then chow plus cookies, etc.).
6. Rat chow plus crackers, cookies, and chocolate all at the same time.  

Adding a palatable food to the cage (crackers, cookies, or chocolate) increased food intake, as expected.  Adding multiple palatable foods at once increased food intake further, suggesting that variety in addition to palatability contributed to food intake.

When rats were fed these diets for 7 weeks, they produced major differences in weight gain:

Consistent with the food intake data, each of the palatable foods increased weight and fat gain, however giving them all at once caused the rats to gain weight and fat at an even higher rate.  We already knew from the "cafeteria diet" studies that easy access to a variety of palatable foods can cause rapid fat gain in rats and humans (3, 4), but this study shows that food variety itself is an important part of the equation.

The results of this experiment show that the simultaneous presentation of a variety of palatable foods can lead to hyperphagia [excessive eating] and the development of obesity.

Food variety is a determinant of the palatability and reward value of the meal as a whole.  However, to be more precise, variety-induced overeating is usually explained by a related phenomenon called "sensory-specific satiety".  The idea is this: as a meal progresses, we get tired of eating specific foods, but being' full' on one food doesn't necessarily mean we want to stop eating another food.  If a variety of foods are present on the table, we tend to eat more total food before feeling satisfied.  There is a large amount of evidence supporting the concept of sensory-specific satiety and its relevance to food intake.

What about the effect of food variety on humans?  A number of trials have shown that increasing food variety increases total calorie intake at a single meal, even if the foods all have nearly identical composition (5).  A study published in 2001 showed that this effect is sustained for at least 7 days in humans (6).  Food variety is probably an important part of why human volunteers overeat and gain weight rapidly on a human "cafeteria diet" (7), and why we tend to overeat and gain fat in the modern food environment, which offers easy access to a huge variety of different foods.

I'll close with a quote from the paper:

In the affluent Western Society, food is presented in a succession of simultaneous variety meals, and in this case, the challenge presented by variety to body weight regulation is much greater and could lead to even greater increases in body weight [than was observed in this study].

Update: "DagherStrength" pointed out on twitter that this helps explain "unbuckle your pants syndrome" at all-you-can-eat buffets.  Good point!