Physical activity and breast cancer risk in women aged 20-54 years.

BACKGROUND/METHODS: Although several studies have suggested that physical activity is associated with a decreased risk of breast cancer, such a decrease has not been found consistently, perhaps because physical activity was assessed in different ways and for restricted periods. Few studies have assessed the risk of breast cancer in relation to lifetime physical activity. We used data from a population-based, case-control study, including 918 case subjects (aged 20-54 years) and 918 age-matched population control subjects, to examine associations between breast cancer risk and physical activity at ages 10-12 years and 13-15 years, lifetime recreational activity, and title of longest held job. RESULTS: Women who were more active than their peers at ages 10-12 years had a lower risk of breast cancer (odds ratio [OR] = 0.68; 95% confidence interval [CI] = 0.49-0.94). Women who had ever engaged in recreational physical activity had a reduced risk of breast cancer compared with inactive women (OR = 0.70; 95% CI = 0.56-0.88). Neither very early recreational activity (before age 20 years) nor recent activity (last 5 years) was associated with a greater reduction in risk than recreational activity in the intermediate period. Furthermore, women who started recreational activities after age 20 years and women who started earlier and continued their activities throughout adult life experienced a similar reduction in risk. Lean women, i.e., women with a body mass index (weight in kg/[height in m](2)) less than 21. 8 kg/m(2), appeared to have a lower risk associated with recreational physical activity than women with a body mass index greater than 24.5 kg/m(2) (OR = 0.57 [95% CI = 0.40-0.82] and OR = 0. 92 [95% CI = 0.65-1.29], respectively). CONCLUSIONS: Our findings support the hypothesis that recreational physical activity is associated with a decreased risk of breast cancer. Physical activity in early or recent life does not appear to be associated with additional beneficial effects.

Visceral fat accumulation in relation to sex hormones in obese men and women undergoing weight loss therapy.

In 70 healthy obese subjects (37 men and 33 premenopausal women; aged 27-51 yr; body mass index, 28-38 kg/m2), associations between the initial amount of visceral fat and sex hormone levels were studied as well as between changes that occurred in response to a 4.2 mJ/day deficit diet for 13 weeks. Magnetic resonance imaging was used to quantify the visceral fat depot. In women, an abundance of visceral fat was significantly associated with diminished levels of sex hormone-binding globulin and free 17 beta-estradiol/free testosterone (T) ratio and to elevated levels of free T after adjustment for age and total fat mass. In men, no significant relationships could be found between visceral fat accumulation and any of the sex hormones. Mean total fat loss was 11.3 +/- 3.3 (+/- SD) kg. In women, loss of visceral fat was significantly related to rises in the sex hormone-binding globulin level and the free 17 beta-estradiol/free T ratio independent of total fat loss, whereas in men, only the association between visceral fat loss and increased estrone level reached statistical significance. In conclusion, in obese premenopausal women, visceral fat predominance seems to be related to a relatively increased androgenicity. In obese men, sex steroid levels appear not to depend on the amount of visceral fat. In obese women, but not in obese men, visceral fat loss seems to be accompanied by a relative reduction in androgenicity.

Imaging techniques for measuring adipose-tissue distribution--a comparison between computed tomography and 1.5-T magnetic resonance.

We developed a method for calculating adipose-tissue areas from transverse body scans by magnetic-resonance imaging (MRI). The method is based on an inversion recovery experiment (repetition time 820 ms, inversion delay time 300 ms, and echo time 20 ms). Total-fat areas and subcutaneous-fat areas were calculated by this method and by computed tomography (CT) from abdominal scans taken in seven male volunteers. The SEE ranged from 4.4 cm2 (CV 4.4%) for subcutaneous-fat areas to 8.3 cm2 (CV 12.8%) for visceral-fat areas. The reproducibility of measuring fat areas with MRI was assessed in seven other volunteers (four males, three females). The average errors of the method for different fat areas were 5.4%, 10.6%, and 10.1% for total-, visceral-, and subcutaneous-fat areas, respectively. We conclude that CT and MRI may yield different absolute values of fat areas (especially visceral fat) but that the ranking of individuals on the basis of their fat areas will be similar by both methods.

Body composition changes assessed by bioelectrical impedance measurements.

Twelve healthy volunteers consumed a very-low-calorie diet for 2 d to achieve a body-weight loss mainly from a loss of fat-free mass, ie, of glycogen plus water. Body weight, body density, and bioelectrical impedance were measured before and after weight loss. Body-weight loss was 1.3 +/- 0.5 kg. Loss of fat-free mass as measured by densitometry was 1.2 +/- 0.8 kg. Changes in body weight and fat-free mass measured by densitometry did not differ significantly and were significantly different from zero. Reduction of fat-free mass as determined by bioelectrical impedance was 0.5 +/- 0.8 kg, which was significantly different from body-weight loss and loss of fat-free mass as measured by densitometry but not significantly different from zero. The results show that after weight loss the bioelectrical impedance method overestimates the fat-free mass by approximately 1 kg.

Effect of a weight cycle on visceral fat accumulation.

Magnetic resonance imaging was used to study the effect of a single weight cycle on three fat depots: the visceral and subcutaneous abdominal depots and the subcutaneous depot at the trochanter level. Obese subjects (17 men, 15 women) were examined before and after weight-loss intervention and 67 wk after intervention. They lost 12.9 +/- 3.3 (mean +/- SD) kg body wt during intervention and regained 11.9 +/- 5.1 kg during follow-up. Weight regain did not result in greater body fatness than before weight loss (initial fat mass: 34.3 +/- 6.1 kg, final fat mass: 32.8 +/- 7.7 kg; P = 0.047). There was no indication of a preferential deposition of visceral fat after weight regain (initial visceral fat area: 120 +/- 41 cm2, final visceral fat area: 110 +/- 48 cm2; P = 0.087). On the contrary, there was a slight tendency to accumulate subcutaneous fat at the expense of visceral fat. It is concluded that weight loss followed by weight regain neither leads to a greater body fatness nor to a larger amount of visceral fat compared with before weight loss.

Waist-hip ratio is a poor predictor of changes in visceral fat.

Magnetic resonance imaging was used to study the effect of weight loss on three fat depots: the visceral and subcutaneous abdominal depots and the subcutaneous depot at trochanter level. Changes in fat depots were compared with changes in circumference measures and the waist-hip ratio (WHR) in obese men (n = 38) and women (n = 40). Mean weight loss was (mean +/- SD) 12.9 +/- 3.5 kg (P < 0.001). The proportional reduction of fat was largest in the visceral depot (men 40%, women 33%). Less fat was lost subcutaneously, especially at trochanter level (men 29%, women 26%). WHR decreased significantly in both sexes (P < 0.001). Change in WHR was not significantly related to the absolute reduction in visceral fat. Total body-fat loss showed a stronger association with subcutaneous fat loss than with visceral fat loss. The findings suggest that fat distribution may change with weight loss, particularly by the loss of visceral fat, but changes in WHR are not appropriate for evaluating changes in this fat depot.

Visceral fat accumulation measured by magnetic resonance imaging in relation to serum lipids in obese men and women.

In 91 apparently healthy obese subjects (45 premenopausal women and 46 men) the associations between specific fat depots and serum lipids were studied. Magnetic resonance imaging was used to quantify fat depots at abdominal and hip level. In women, an accumulation of visceral fat was associated with a less favourable lipid profile, even after adjustment for age and body fat percentage: higher triglycerides levels (P less than 0.001), lower levels of HDL-cholesterol (P less than 0.01) and a diminished HDL-cholesterol/LDL-cholesterol ratio (P less than 0.01). In men, however, the significant inverse relationship between an abundance of visceral fat and the HDL-cholesterol/LDL-cholesterol ratio and the significant positive correlations with total-, LDL-cholesterol and triglycerides disappeared after adjustment for age and fat percentage. Within each sex, subcutaneous fat neither at abdominal level nor at hip level was significantly related to serum lipids. It is concluded that there are gender differences in the associations between visceral fat accumulation and serum lipids.

Body mass index as a measure of body fatness in the elderly.

Body composition was assessed in a group of 35 apparently health elderly males and 37 elderly females, aged 60-83 years, by means of anthropometry and densitometry. Mean body mass index (BMI) of the males was 25.0 +/- 2.2 kg/m2 and of the females 25.9 +/- 3.2 kg/m2, which indicates normal weight to only minor overweight. Body fat as assessed by densitometry was 31 per cent in men and 44 per cent in women, a rather high value, especially when compared to the rather low BMI. Body fat percentage as calculated from the sum of four skinfolds (bicipitalis, tricipitalis, subscapularis and supra-iliacalis) using regression equations from the literature was 27.9 +/- 2.5 per cent and 38.7 +/- 3.2 per cent for men and women respectively. These values are probably an underestimation of the body fat, due to a higher proportion of internal fat in elderly subjects, which is not measured by skinfolds. Body fat percentage as determined by the BMI has an estimation error of about 4 per cent when derived from sex- and age-specific regression equations. The body fat percentage as predicted from skinfold thicknesses had a comparable error of estimate. These prediction errors in the body fat percentage in the elderly are comparable with the prediction errors found in young and middle-aged subjects as reported in the literature.

Factors affecting bioelectrical impedance measurements in humans.

In several groups of young healthy subjects the effect of the ingestion of a meal, of drinking normal tea or beef tea, of exercise and of the menstrual cycle on body impedance was assessed. The day-to-day reproducibility of the method was also investigated under standardized conditions. Two to four hours after ingestion of a meal, body impedance had decreased by about 13-17 Ohms in comparison with body impedance in the fasting state. Drinking 200 ml of normal tea did not result in a change of body impedance, but drinking 200 ml beef tea lowered the body impedance significantly by 4 +/- 4 Ohms. Moderate exercise on a bicycle ergometer (90 min, 100 W) did not influence body impedance, but strenuous exercise (90 min, 175 W) resulted in a decrease of 9 +/- 11 Ohms in body impedance. In general, changes in body impedance during the menstrual cycle were small, and only the difference between measurements of body impedance 1 week before the onset of the menstruation and again 1 week after menstruation (8 +/- 9 Ohms) was statistically significant. Under standardized conditions (in the morning, in the fasting state after emptying the bladder) the within-person between-day variation was found to be 2.8 per cent (13 Ohms).

Is an adaptation of Siri's formula for the calculation of body fat percentage from body density in the elderly necessary?

Using data from the literature on changes in the mineral content, muscle mass and the amount of water in the body during aging, the age-related changes in the chemical composition of the fat-free mass have been calculated. In men the decrease in minerals (bone loss) during aging equals the decrease in protein and water (muscle) in the fat-free mass. As a consequence the chemical composition of the fat-free mass is hardly affected by aging in men. In women, however, the loss of minerals during aging is considerably higher than the decrease in protein and water in the fat-free mass. As a consequence the change in the chemical composition of the fat-free mass in females is remarkable, and therefore in females, the density (kg/l) of the fat-free mass decreases with age. Consequently the body fat percentage calculated from body density with Siri's equation overestimates the real body fat percentage by 2-3 per cent, depending on age. Based on the calculated chemical composition of the fat-free mass at several ages, and its calculated theoretical density, Siri's equation has been adapted. In females but not in men the adapted formulas give a more valid estimate of the body fat percentage calculated from body density compared to Siri's formula.

In obese subjects the body fat percentage calculated with Siri's formula is an overestimation.

By means of theoretical calculations it is shown that the chemical composition of the fat-free mass is affected by the amount of fat in the body. With increasing fatness the relative amounts of minerals and protein in the fat-free mass will decrease and the relative amount of water will increase. These changes in the chemical composition of the fat-free mass are confirmed by data from the literature. Because minerals and protein are the most dense components in the fat-free mass, and water is the less dense component, the density of the fat-free mass will decrease with increasing body fatness. As a consequence, the normally used computation formula for the calculation of the body fat percentage from whole-body density (Siri's equation) will systematically overestimate the real body fat percentage by as much as 2-4 per cent in severely obese subjects. This overestimation is large enough to correct for in studies on energy metabolism and body composition.

Assessment of body composition in 8-11 year old children by bioelectrical impedance.

In 64 prepubescent schoolchildren, 33 boys and 31 girls, aged 8-11 years, body composition was measured by means of anthropometry, densitometry and bioelectrical impedance. From body density the body fat percentage was calculated using age-specific density values for the fat-free mass. Boys and girls younger than 10 years did not differ in body composition. Older boys however had higher body weights, higher body densities and lower body impedance values. Fat-free mass as determined by densitometry could be predicted by body impedance and body weight with a prediction error of 1.31 kg. The prediction formula was sex-specific. Omitting the impedance in the prediction equation resulted in a 7 per cent lower explained variance and an only slightly higher prediction error of the FFM of 1.65 kg. The prediction formulas from the literature, developed in adult populations, grossly overestimated the fat-free mass in children, probably due to a different water distribution between the intra- and extra-cellular spaces.

Body impedance is largely dependent on the intra- and extra-cellular water distribution.

Electrical impedance measurements were performed in fasting blood samples and analysed in relation to packed cell volume and calculated intra- and extra-cellular water distribution. The total blood impedance was shown to be strongly dependent on the ratio of intra-cellular water to total water (r = 0.97, P less than 0.0001). In a group of 515 subjects, with a large variation in age and body composition, the relation between the body impedence corrected for fat-free mass and body height (the specific body impedance) and the calculated ratio of intra-cellular water to total body water, was found to be similar to that in blood. From these observations a regression model was developed and applied to body compositional data of several groups of subjects before and after weight loss caused by water losses. It was possible to calculate at a group level the losses of intra- and extra-cellular water, which confirms the applicability of the model. It is concluded that the validity of the predicted fat-free mass or total body water from body impedance is largely dependent on the water distribution in the measured subjects. This means that age- and sex-specific prediction formulas have to be used for the assessment of the body composition and that the bio-electrical impedance method is only with caution applicable in subjects with a disturbed water distribution as in oedema, pregnancy and dehydration.

The effect of psychological stress on diet-induced thermogenesis and resting metabolic rate.

The effect of psychological stress on resting metabolic rate (RMR) and diet-induced thermogenesis (DIT) was assessed in 12 healthy young non-obese men of body weight 70.2 +/- 1.2 kg (mean +/- s.e.m.) and age 25 +/- 0.6 years. Two types of commercially available motion pictures (video films) were shown to the subjects during the measurements, ie stress-inducing horror films and as a control, romantic family films. The study was conducted according to a cross-over design. RMR and respiratory quotients were not significantly influenced by the type of film shown to the subjects. DIT, assessed over 4 h, was significantly increased by the stress-inducing treatment, 0.95 +/- 0.05 kJ/min (mean +/- s.e.m.) versus 0.76 +/- 0.06 kJ/min (control). No significant effect was observed of psychological stress on postprandial substrate oxidation rates, nutrient balances, and urinary catecholamine excretion.

Techniques for the measurement of visceral fat: a practical guide.

The measurement of fat distribution has become an important issue in obesity research. Numerous techniques have been developed to assess visceral fat because this fat seems to be most strongly associated with metabolic disorders. This review focuses on methods for the direct and indirect assessment of visceral fat ranging from multiple-scan computerized tomography to anthropometric measurements. The principles of techniques, their accuracy and reproducibility as well as aspects of costs and safety are discussed. Comparison of the different methods shows that imaging techniques, such as computerized tomography and magnetic resonance imaging, are the optimal techniques available for accurate assessment of visceral fat. Methods other than imaging techniques have limited potential in the measurement of changes in visceral fat deposition. Anthropometric measurements can be useful to classify subjects into different types of fat distribution for diagnosis of abdominal obesity, and for general application in epidemiological studies. The choice of a particular technique should be based on a balance of practical and financial considerations and the aim of the study. Involvement of ionizing radiation exposure may be an important element in the decision-making process.

Circadian rhythms of appetite at different stages of a weight loss programme.

A group of 28 healthy obese people (16 women, 12 men) rated their appetite each whole hour of the day during nine separate days at three different stages of a dietary intervention study of 24 weeks. The first stage was an introduction period of eight weeks in which subjects were weight stable. The second stage was a weight reduction period of 13 weeks in which subjects lost about 0.85 kg/week of body weight. In the third stage of three weeks subjects were weight stable again. The slimming diet, which contained predominantly sweet items, had an energy content which was 1000 kcal (4.2 MJ) below the individually estimated daily energy expenditure. The results showed that appetite for a meal increased in the first week of the weight reduction period of 13 weeks but returned to the baseline level within 4-8 weeks. Appetite for something savoury remained elevated during the entire weight reduction period, and returned to the baseline level in the stabilization period. Appetite for something sweet did not change. The circadian rhythms of the different types of appetite remained unchanged at all stages during the diet intervention programme. Different types of appetite (e.g. sweet, savoury) had different patterns over the day.

Abdominal diameters as indicators of visceral fat: comparison between magnetic resonance imaging and anthropometry.

The aim of the present study was to investigate the usefulness of abdominal diameters to indicate visceral fat, their relationship with serum lipids and their capability of detecting changes in visceral fat. Before and after weight loss, visceral and subcutaneous fat, and the sagittal and transverse diameters were assessed by magnetic resonance imaging (MRI) in forty-seven obese men and forty-seven premenopausal obese women with an initial body mass index of 31.0 (SD 2.4) kg/m2. In a subsample (n 21), diameters, were also measured by anthropometry in the standing and supine positions. They were strongly correlated with the diameters derived from the MRI scans. Serum levels of total and HDL-cholesterol and triacylglycerol were measured before weight loss. In women the sagittal diameter correlated less strongly with visceral fat than anthropometrically-assessed waist circumference and waist:hip ratio (WHR). In men these associations were comparable. Changes in visceral fat with weight loss were more strongly correlated with changes in the sagittal diameter and sagittal:transverse diameter ratio (STR) than with changes in waist circumference or WHR in men. In women, changes in the anthropometric variables and the separate diameters (except STR) were not associated with visceral fat loss. In men, but not in women, both the sagittal diameter and the visceral fat area were related to serum lipids. It is concluded that the sagittal diameter and STR may have advantages over waist circumference and WHR in men, particularly in assessing changes in visceral fat, but this could not be demonstrated in women. The ability to predict visceral fat from circumferences and diameters or their ratios is, however, limited in obese men and women.