Here in America, weight loss and dieting seem to go hand-in-hand. However, the notion that you can’t achieve weight loss without restrictive dieting has been shown time and again to be wrong. In fact, studies have proven that the long-term result of dieting may actually be the opposite of the intended goal – i.e., weight gain.
There are a few reasons for this. First, when you restrict certain foods or food categories, like carbohydrates, it can lead to strong cravings for that particular food, which can eventually trigger overeating. Second, restrictive dieting messes with your metabolism and leads to the loss of lean muscle mass, both of which cause post-diet weight gain.
Interestingly, research has uncovered a genetic component to both body mass index (BMI) and intentional weight loss (meaning the weight you intentionally try to lose, as opposed to losing weight, for instance, while sick). Therefore, it is possible that the people most genetically prone to obesity end up dieting more, and subsequently gain the most weight after they are done dieting.
Researchers in Finland wanted to explore this idea a little further using twins as subjects.
They followed 4,129 individual twins (1,922 males and 2,207 females) from the FinnTwin16 study. Specifically, they studied “intentional weight loss discordant” identical twins (meaning one twin was trying to lose weight while the other wasn’t). They also looked at the weight development of intentional weight loss discordant fraternal twins, and identical and fraternal twins with the concordant (or the same) dieting history, to determine what role, if any, genes played in dieting.
Do Genes Play a Role in Your Jean Size?
Researchers obtained information about these twins at ages 16, 17, 18 and 25. At each of these surveys, they were asked about height, weight, health habits, general health, and social relationships. At age 25, they were also asked about the number of lifetime intentional weight loss episodes of at least 5 kg (approximately 11 lbs). Other factors taken into account included physical activity, smoking, frequency of breakfast eating, number of children, BMI of parents, and socioeconomic status.
Analyses of these data revealed some interesting findings.
Thirty-eight percent of females and 24 percent of males reported having one intentional weight loss episode of 5 kg or more during their lifetimes. And 15 percent of females and 10 percent of males had two or more intentional weight loss episodes.
Not taking genetic factors into consideration, body mass index at age 16 was a huge factor in determining future intentional weight loss episodes.
Interestingly, both men and women who had no intentional weight loss history weighed significantly less than men and women who had any number of intentional weight loss episodes. In fact, the people with no intentional weight loss had the least amount of weight gain, while those who had five or more intentional weight loss episodes had that largest weight gain.
When genetic factors were taken into account, both the identical and fraternal twins of the same sex had similar body mass index development between ages 16 and 25, regardless of whether they dieted. Twins who did have a history of intentional weight loss were heavier at all ages and gained more weight than those twins who had no such history.
In the identical twins, at age 16, weights were similar. At age 25, identical twins with intentional weight loss were slightly, but not significantly, heavier than identical twins who did not have intentional weight loss. This suggests that dieting is associated with weight gain later in life, regardless of genetics.
In the fraternal twins, the twins who had intentional weight loss were heavier at all ages than twins without intentional weight loss. According to researchers, these results suggest “the need to diet only arises in [twins] who are more genetically predisposed to obesity.”
The researchers concluded, “The results presented show that twin pairs where both [twins] have intentional weight loss episodes are heavier throughout their adolescence and young adulthood than pairs where neither of the [twins] had intentional weight loss.”
What Does This Mean For You?
In simple terms, what this study aims to prove is that regardless of your genetic makeup, strict, restrictive dieting can, and usually does, have negative long-term weight gain effects.
Think about the last time you tried a fad diet. Sure, you lost weight initially. You may have even lost a large amount of weight quickly. But what happened when you stopped dieting? Most likely, that weight you lost piled right back on… and possibly even more.
The point is, in order to lose weight and keep it off, you should not be following a diet that deprives you of foods from important food groups (like whole grain carbohydrates).
Instead, you should be following a sensible eating plan that is well-rounded and includes a variety of foods from all food groups. One such eating plan, which has been shown to be extremely heart-healthy and promote weight loss without making you feel deprived, is the Mediterranean diet.
As a bonus, if you eat healthfully and sensibly the majority of the time, the occasional dessert or sugary treat likely won’t affect your waistline or the scale. And, of course, when it comes to healthy weight loss, exercise is just as important as what you eat. Be sure to work out as often as possible, ideally at least 30 minutes, five days a week.
 Pietilainen KH, Saarni SE, Kaprio J and Rissanen A. Does dieting make you fat? A twin study. International Journal of Obesity. 2012;36:456–464.