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Cognitive dietary restraint, food intake and cortisol excretion in premenopausal women

University of British Columbia

In order to achieve or maintain a desired body weight many women consciously try to limit their food intake. This is referred to as dietary restraint or cognitive dietary restraint. Currently the instrument most commonly used to assess dietary restraint is the restraint scale of the Three-Factor Eating Questionnaire (TFEQ). Previous studies have found women with high restraint scores to be similar to those with low restraint scores in terms o f age, Body Mass Index (BMI), and energy intake. Where a difference has been found is in menstrual cycle, and particularly ovulatory, characteristics. While the mediating mechanism for this association is not known we have hypothesized that women with high restraint scores may experience more stress as a result of monitoring their food intake. Stress, whether physiological or psychological, activates the hypothalamic-pituitary-adrenal axis resulting in an elevation in serum Cortisol and consequently, in urinary Cortisol excretion. Higher levels of Cortisol are associated with a decrease in reproductive hormones and also with accelerated bone loss. This cross-sectional study was designed to determine whether relationships exist among dietary restraint, food intake, Cortisol excretion and bone mineral density (BMD) in premenopausal women. To address this purpose a two-part study was designed. In Part One, women completed a survey instrument which included the TFEQ, Eating Disorder Inventory (EDI), Rosenberg's Self-esteem Scale and Perceived Stress Scale as well as information on physical, lifestyle and menstrual cycle characteristics. Individuals from Part One were recruited for Part Two on the basis of having low or high restraint scores and a number of other inclusion/exclusion criteria. Eligible participants were 20-35 y, weight stable, had a BMI between 18 and 25 kg /m , exercised < 7 hr/wk, were regularly menstruating and not using oral contraceptives. These individuals completed 3-day food records, collected a 24- hour urine specimen on a day in which all food was provided to them and their intakes recorded, and had their body composition and BMD assessed by DEXA. Participants (n = 666) in Part One were grouped on the basis of restraint scores into low, medium or high restraint groups. The 3 groups were similar in average age, height, weight and BMI, but women in the high restraint group had higher 'highest' BMIs, exercised more (hr/wk) and were more likely to report following vegetarian diets. Also, a greater proportion of women with high restraint scores reported presently trying to lose weight, had ever tried to lose weight, had a history of eating disorders and had experienced weight fluctuations. A significant difference was found in menstrual cycle regularity with 34% of women with high restraint scores reporting irregular cycles compared with about 17% of women with low or medium restraint scores. Scores on the TFEQ hunger scale and EDI maturity fears scale did not differ among groups, but women in the high restraint group had higher scores than those in the low restraint group on all other psychometric scales. Overall, Part One provides a broad profile of the study population from which Part Two participants were recruited. Participants (n = 62) in Part Two were also compared on the basis of high or low restraint scores. Again, age, height, weight and BMI were similar. Both 3-day reported and 24-hour documented energy and fat intakes were lower in the high restraint group, but other nutrient intakes, including calcium, were similar. Exercise level was higher in the high restraint group although the inclusion criterion was set at < 7 hr/wk. The 24-hour urinary excretion of Cortisol in women with high scores for restraint was significantly greater than in women with low scores for restraint. There were no associations between Cortisol excretion and energy or nutrient intakes or exercise level. Characteristics of bone did not differ between restraint groups but further analysis using exercise as a covariate revealed lower values for bone mineral content (BMC) in the high restraint group. Differences were found in BMD and BMC between women grouped as minimal (0-< 2 hr/wk) or moderate (2-7 hr/wk) exercisers with the latter having higher values. Later analysis of only women who reported exercising moderately revealed lower values for total body BMC and spinal BMC in women with high compared to low restraint scores. The finding that urinary Cortisol excretion was higher in women with high scores for dietary restraint than those with low scores is unique and supports our hypothesis that dietary restraint is a stressor with corresponding physiological responses from the neuroendocrine system. Higher Cortisol excretion has long term implications for bone health; accordingly our results suggest that dietary restraint may not be innocuous. Our study concurs with other cross-sectional studies in finding a difference in BMC and BMD between minimal and moderate exercisers. What our results add is the finding that within women grouped as moderate exercisers, high levels of dietary restraint may be a limiting factor in the maximization or maintenance of bone mass, possibly through associated higher Cortisol levels. Prospective studies are needed to determine whether the cross-sectional associations among dietary restraint, Cortisol, moderate exercise and bone mineral characteristics persist over time.

Thesis/Dissertation

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2009-07-03

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http://hdl.handle.net/2429/10034

Family and Nutritional Sciences

University of British Columbia

UBCV

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