Recent research indicates that there may be additional detrimental impacts for health for yo-yo dieters. Review International Journal of Obesity article Weight cycling during growth and beyond as a risk factor for later cardiovascular diseases: the ‘repeated overshoot’ theory 28/11/06
1) Which population groups are most likely to fall into a yo-yo dieting cycle?
Studies have shown that those that are overweight or obese are likely to have tried to lose weight at least once. As the incidence of childhood obesity increases so too does the incidence of younger people being caught in the yo-yo dieting cycle.
Adults that are underweight or of a normal weight range have been reported as making the decision at least once to diet with a higher recorded occurrence of dieting in the younger group. This is often due to being unhappy with the way that they look based upon media pressures. These pressures are becoming noticeable and are influencing much younger audiences both male and females under the age of 16.
Yo-yo dieting may also be undertaken as part of an athlete’s schedule of fitness; to lose or gain weight in preparation for an event and the reverse to occur after the event. Involuntary dieting may also take part during periods of chronic illness or when food isn’t freely/ regularly available.
So, most commonly, girls and young women are most likely to fall into a pattern of yo-yo dieting, represented by those that have an overweight BMI but more increasingly by those of a normal BMI.
2) In what ways does yo-yo dieting put additional strain on the cardiovascular system?
Yo-yo dieting puts a strain on the cardiovascular system and the following risk factors are now known:
a. Increased weight gain. Following a period of weight loss, as part of a yo-yo cycle, the weight gain has been reported to be higher than that originally lost. Although this isn’t reported in all cases it has been seen across a variety of population studies. Weight gain is known to increase the risk of cardiovascular disease.
b. Greater body and visceral fat deposits. A few human studies have shown that yo-yo dieting affects body composition by reducing lean tissue and increasing body or visceral fat for women. In studies using rats the evidence was more conclusive showing that the more cycles of weight gain and loss that the animal was put through the more likely and higher the levels of fat were deposited. In humans the link may be that while total body composition doesn’t change, the redistribution of fat largely to the abdominal area does occur, particularly for obese women. Fat deposited in this area is already linked to an increased risk of cardiovascular disease. The study showed that for non-obese women that were yo-yo dieters the link was significantly greater.
c. Changes to the composition of tissue lipids. There are studies which have shown that the fat deposited changes its composition. In rats on yo-yo diet cycles the fats analysed showed an increase in saturated fat and a decrease in polyunsaturated fats. This is thought to occur because saturated fat stores are easily replenished but the polyunsaturated fats (essential fatty acids) are not and are obtained from the food eaten so during weight loss the correct balance of food may not be eaten. A low level of essential fatty acid (notably linoleic acid) in adipose tissue is linked to a higher risk of cardiovascular disease.
d. Insulin resistance and type 2 diabetes. Research has shown that people experiencing larger changes to their weight (as seen in yo-yo dieting) showed a greater insulin resistance with a significantly higher correlation shown in those with a normal BMI compared to overweight BMI. This can result in a greater increase in diabetes developing either directly from yo-yo dieting or from the process of gaining more weight during the gain phase of dieting.
e. Dyslipidemia (abnormal amount of lipids in the blood). A study of women with a history of yo-yo dieting had much lower HDL-C (‘good cholesterol’) levels than those that didn’t diet. The same results were found with men reported to have an increased risk of cardiac disease. Having less HDL-C or an increase in LDL-C (‘bad cholesterol’) is a proven factor that increases the risk of cardiovascular disease.
f. Hypertension (high blood pressure). Studies with rats demonstrated that blood pressure increases during the weight gain part of the yo-yo diet cycle but this isn’t usually long lasting. Reports with human subjects showed that there is a direct link between weight gain; an increase in BMI and an increase in blood pressure. At night we should experience a decrease in blood pressure, those that don’t are known to be at greater risk of cardiovascular disease. It is possible that weight gain disrupts this normal occurrence exposing yo-yo dieters to these risks.
g. The repeated overshoot theory. The likelihood of a person developing cardiovascular disease increase the more fluctuations of the above risk indicators occur. Repeated overshoots, during weight gain period, of blood pressure and heart rate put extra stress on the heart and blood vessels. The changes to kidney functions (glomerular hyperfiltration) during weight gain periods of the yo-yo diet cycle put a person at higher risk of experiencing changes to blood lipids and to circulating the inflammatory cytokines therefore increasing the likelihood of developing cardiovascular disease. Fluctuations can also lead to vascular damage through the changes in cholesterol, glucose and triglycerides levels in the blood.
3 Considering the cardiovascular impact, as well as the strong link to increasing obesity, should we consider yo-yo dieting a major public health issue?
Yo-yo dieting is definitely a concern for public health. There is an increase in the occurrence of young people, particularly girls and women, being influenced by social pressures to alter their appearance and conform to an ‘accepted’ norm. Starting this yo-yo diet cycle at a much younger age and in people within a normal BMI range increases the range of the population at risk from cardiovascular disease by exposing them to the physical changes within the body from multiple periods of weight gain.
Children and parents need to be aware of the dangers of dieting and how to provide a balanced and healthy diet. Additionally, changes need to be made to the advertising of unhealthy foods and lifestyles. Finally, the portrayal of airbrushed, filtered models as the normal or average body shape needs to change to remove pressures people feel to yo-yo diet.