To clarify the pathogenesis of altered bone and mineral metabolism in diabetes, biological markers for osteoblastic and osteoclastic function were measured in patients with type 2 diabetes. A significant reduction of serum osteoblastic markers was found in the diabetic group, whereas circulating and urinary levels of osteoclastic markers in the diabetics were significantly higher than in the controls. Unexpectedly, serum levels of osteoprotegerin (OPG), a known osteoblast-derived bone coupling factor that inhibits osteoclastgenesis, tended to be higher in the diabetic group, and these values exhibited a significantly positive correlation with those of osteoclastic, but not osteoblastic, markers. In addition, there was a significantly negative correlation between serum OPG and bone mineral density. It seems probable that OPG exerts a suppressive and protective role against increased bone resorption to prevent further loss of skeletal bone mass under conditions of reduced osteoblastic function in type 2 diabetes. The increase in osteoclastic function would be at least partly due to acceleration of the polyol pathway, possibly leading to enhanced endogenous oxidative stress under hyperglycemic conditions. Elucidation of the precise mechanisms responsible for altered bone and mineral metabolism in the diabetic state will be very important for prevention and treatment of bone mass loss to preserve the quality of life of diabetic patients, in view of the increasing number of aged diabetics in Japan, who would be expected to develop diabetic osteopenia, and thus have a high risk of bone fracture.

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We previously reported that fish oil is nutritionally less desirable than lard and soybean oil. In the present study, to investigate the reasons for this, three groups of 4-week-old male Fischer 344 rats were fed one of three diets: a lard diet, a soybean-oil diet or a fish-oil diet (experimental period). After 8 weeks, all rats were placed on a self-select regimen and allowed to choose a lard diet or a fish-oil diet for 3 weeks (self-selection period). After the experimental period, plasma lipid concentrations were lower in the fish-oil diet group than in the other two groups. At the beginning of the self-selection period, the ratio of the fish-oil diet intake [fish-oil diet intake (g) /total intake (g)] was highest in rats fed the lard diet and lowest in rats fed the fish-oil diet. However, the ratio in rats fed the lard diet and the soybean-oil diet decreased, and that in rats fed the fish-oil diet increased gradually, so that by the 7-9th day of the self-selection period no significant difference in the ratio was evident among these three groups. After the self-selection period, no significant difference in the plasma lipid concentration was observed among these three groups. Therefore, these 3 groups of rats counteracted the shortage of fatty acids at the beginning of the self-selection period and then self-selected the lard diet and the fish-oil diet to maintain n-6/n-3=3. These findings suggest that rats have an ability to consume a lard diet and a fish-oil diet to obtain an adequate ratio of essential fatty acids.

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Obesity is usually diagnosed on the basis of body mass index (BMI). Obesity, however, is defined as excessive fat volume, and not merely as being overweight. In the present study we measured BMI as well as body composition by bioimpedance analysis (BIA), and studied their relative contribution in defining obesity. BMI exhibited an almost linear correlation with fat volume, but only a modest correlation with lean body mass (LBM). The correlation of BMI with LBM was less marked in subjects with BMI ≥25 kg/m² than in those with BMI <25 kg/m². For the diagnosis of obesity based on body composition (percentage fat volume ≥20% for males and ≥30% for females), BMI had high specificity, but low sensitivity. In other words, a BMI exceeding 25 kg/m² is almost always associated with obesity based on body composition. A lower BMI, however, does not rule out the presence of obesity based on body composition. Thus, nutritional assessment would be more effective if based on both BMI and body composition.

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The use of carmine as a balance study marker was evaluated. Twenty-four male Fischer rats were preliminarily maintained for one week on an AIN-93G diet and then divided into four groups. Two kinds of experimental diet were administered: a AIN-93G (M) diet (Con) and a sucrose diet (Suc), in which the source of carbohydrate was sucrose alone. Also, two kinds of balance study method were employed: a marker-use group (M) and a non-marker group (NM). The first balance study was carried out just after preliminary maintenance (I), and the second to fifth balance studies (II, III, IV, and V) were conducted in the third week, fifth week, fifth month and seventh month of the experiment. The M groups were given a 0.1% carmine diet (red diet) on the first and last days of the balance study, and red feces and white feces were collected separately on the following day. All feces during the balance study in the NM groups were collected. It was found that the feces on each day of the balance study included feces derived from the diet admininstered two days before, and the proportion of these feces increased with advancing age. In balance study I, the dry fecal weight per unit food intake in the SucNM group was significantly lower than that in the SucM group, and high calcium absorption was observed in the SucNM group. In the other balance studies, there was no difference between the M and NM groups. These results show that a marker is needed when a balance study is conducted immediately after a diet regime has been started, or for comparing a diet among animals of different ages. When the same diet is supplied continuously under conditions such as constant feeding and constant fecal excretion, it is possible to conduct a balance study without a marker.

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