their weight until they hit a bump in the road of life,
then they turn to food to reduce their stress, starting
the yo-yo cycle. Boredom, loneliness, and frustra-
tion also cause people to eat when they are not truly
hungry.
psychological factors. Many people start a diet with
unrealistic expectations about how much weight they
will lose, how fast the weight will come off, how
much effort it will take, and how many permanent
lifestyle changes they will have to make to keep the
weight off. These attitudes all influence whether the
individual will weight cycle. In addition, people who
weight cycle are more likely to have depression and
to be binge eaters with impulse-control issues.
social factors.Many social events revolve around eat-
ing. People who feel they need to eat to please others
or who have impulse-control difficulties often eat
more than they intend in social situations. The trend
toward super sizing restaurant portions reinforces
the tendency to eat too much in social settings.
Activity level. Studies show that people who are diet-
ing consistently underestimate how many calories
they burn in exercise. In general, the more active a
person is, the easier it is for her to maintain a weight
loss.
Lack of nutritional information. Studies show that
people consistently underestimate how many calories
they eat and overestimate the amount of food that
makes up a healthy portion. Although people who are
successful in keeping weight off for many years tend
not to strictly count calories, they are very aware of
what and how much they eat.Research on weight cycling
Starting in the 1980s researchers began testing a
theory called the ‘‘set point’’ theory of weight cycling.
This theory suggested that each individual has a natu-
ral set point for weight to which the body always tries
to return. To explain this, researchers have suggested
that the body has feedback mechanisms that adjust the
metabolic rate so that fat stores are maintained at a
relatively constant level.
The set point theory of weight cycling was first
tested on weight-cycling mice that were made obese
and then put on a diet more than once. Researchers
found that when mice were fed a normal diet after
losing weight on a calorie-restricted diet, they gained
back the weight they had lost and more, and that
during a second round of dieting, it took them longer
to lose the weight that they had gained. This seemed to
support the set point theory. However, research needed
to be done on humans to prove the theory.Doing a well-controlled weight cycling study on
humans is difficult. It is unethical to manipulate the
weight of volunteers the way the weight of laboratory
animals is manipulated because there are clear and
undisputed health risks to being overweight. Instead,
researchers must depend on volunteers who self-report
weight-cycling in the past. In addition, studies must
compensate for differences in age, gender, health his-
tory, activity, and other lifestyle factors that are not an
issue with laboratory animals. Some of the most
tightly controlled human studies were done as inpa-
tient studies where obese individuals were put very low
calorie diets (less than 450 calories per day) under
medical supervision to stimulate rapid weight loss.
This type of extreme dieting does not necessarily
reflect the way the majority of people diet in the real
world. Given the variety of factors that affect human
studies of weight cycling, it is not surprising that
results concerning the effect of weight cycling on
health are conflicting.
Several small studies done in the mid 1990s found
that metabolic rate, or the rate at which a person burns
calories, decreased after weight loss, supporting the set
point theory. Later, more rigorously controlled stud-
ies found that after a temporary initial decrease, meta-
bolic rate returned to pre-weight loss values. Based on
these more recent findings, the National Institutes of
Health takes the position that it should not be harder
to lose weight when dieting after weight cycling. How-
ever, as people age they burn calories more slowly.
This natural slowing of metabolism may make it
appear that it becomes harder and harder to lose
weight after several cycles of yo-yo dieting.
Other studies have looked at whether people who
gain back the same amount of weight as they have lost
have a higher percentage of body fat than they did
before they weight cycled. In other words, did they lose
muscle, but gain back fat? Researchers have found that
people gain back muscle and fat in the same propor-
tion that they had before they dieted, but that in some
people the fat is distributed differently in their body.
In these people weight cycling tends to put more fat
back on the stomach and less on the thighs and but-
tocks. This may have health implications, as people
who have more fat in the stomach area are more likely
to develop type 2 (adult-onset) diabetes.
Other studies have looked at the effect of weight
cycling on the development of heart disease andgall-
stones, and on immune system functioning. Gall-
stones are hard, painful masses of cholesterol and
calciumthat form in the gallbladder and bile ducts.
Some studies have found that people who weight cycle
are more likely to develop gallstones. ResearchWeight cycling