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Effects of Diet-Induced Moderate Weight Reduction on Intrahepatic and Intramyocellular Triglycerides and Glucose Metabolism in Obese Subjects

Departments of Medicine, Metabolism and Endocrinology (F.S., Y.Tam., H.W., N.K., Y.I., H.U., T.H., Y.Tan., R.K.), Radiology (T.M., S.K.), and Cardiology (S.S., H.S.), Juntendo University School of Medicine, 113-8421 Tokyo, Japan

Address all correspondence and requests for reprints to: Yoshifumi Tamura, M.D., Department of Medicine, Metabolism, and Endocrinology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan. E-mail: ys-tamur{at}med.juntendo.ac.jp; or Yasushi Tanaka, M.D., Division of Metabolism and Endocrinology, Department of Medicine, St. Marianna University School of Medicine, Kawasaki, Japan. E-mail: y2tanaka{at}marianna-u.ac.jp.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Context: Although moderate weight reduction is recommended as primary therapy of metabolic syndrome, little information is known regarding metabolic changes associated with moderate weight reduction in nondiabetic obese subjects.

Objective: The aim of this study was to determine the effects of a moderate weight reduction program on intracellular lipid and glucose metabolism in muscle and liver.

Participants: Data for 13 nondiabetic obese subjects were evaluated.

Intervention: Subjects were put on a 3-month mildly hypocaloric diet therapy (35 kcal/kg of ideal body weight).

Main Outcome Measures: Intrahepatic lipid (IHL) and intramyocellular lipid were measured by using ¹H magnetic resonance spectroscopy. Peripheral insulin sensitivity and splanchnic glucose uptake were evaluated by euglycemic-hyperinsulinemic clamp with oral glucose load.

Results: Diet therapy for 3 months resulted in 6% reduction in body weight (from 99.9 ± 7.3 to 93.8 ± 6.6 kg, P < 0.0001). This change was accompanied by reduction of plasma glucose and insulin excursions during 75-g oral glucose tolerance tests, decrease in diastolic blood pressure, glycated hemoglobin, serum low-density lipoprotein cholesterol, and triglyceride. These changes were also accompanied by a decrease in IHL (from 12.9 to 8.2%, P < 0.01) and increase in splanchnic glucose uptake (from 13.5 to 35.0%, P < 0.03). On the other hand, the diet program did not affect intramyocellular lipid or glucose infusion rate during euglycemic hyperinsulinemic clamp.

Conclusions: Our results suggest that moderate weight reduction in obese subjects decreased IHL and augmented splanchnic glucose uptake. This mechanism is at least in part involved in improvement of glucose metabolism by moderate weight reduction in obese subjects.

	Introduction

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THE INTERNATIONAL DIABETES FEDERATION recently recommended moderate weight loss (5–10%) by lifestyle modification as a primary therapy of metabolic syndrome (1). It is widely known that moderate weight reduction improves the risk factors of cardiovascular disease (2). Importantly, moderate weight loss also improves insulin resistance and central obesity, which is located upstream of the metabolic syndrome (3).

Recent data suggest that intracellular lipids in muscle and liver are associated with insulin resistance. Cross-sectional studies using ¹H-magnetic resonance spectroscopy (¹H-MRS) or biopsy specimen have demonstrated that the intramyocellular lipid (IMCL) is associated with insulin resistance in skeletal muscle (4, 5). Hepatic insulin sensitivity was negatively correlated with the IHL content (6, 7). We found that 2 wk of diet with exercise decreased IMCL and increased muscle insulin-mediated glucose uptake, whereas diet with or without exercise decreased IHL by about 25% in type 2 diabetes (8). In addition, our preliminary data suggested that splanchnic glucose uptake (SGU) was improved concomitant with decreased IHL (8). Furthermore, Petersen et al. (9) also demonstrated that moderate weight reduction by moderate hypocaloric very-low-fat diet (3%) results in a decrease in IHL and amelioration of hepatic insulin resistance in type 2 diabetes. These data suggest that insulin resistance may be caused by intracellular lipid accumulation in the insulin target organs, and lifestyle modification may reverse these factors.

The present study was designed to determine the effect of moderate weight reduction on intracellular lipid, peripheral insulin resistance, and SGU in nondiabetic obese subjects. In this study, moderate body weight loss was achieved by calorie restriction for 3 months.

	Subjects and Methods

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Experimental subjects and study design

The study subjects were 17 nondiabetic, weight-stable obese men with body mass index (BMI) of more than 30 kg/m². All subjects gave written informed consent to the study, which was approved by the Ethics Committee of Juntendo University. No subjects were taking any medications known to affect glucose metabolism.

Subjects were fasted overnight from 2100 h to 0800 h before each baseline measurement. Seventy-five-gram oral glucose tolerance test (OGTT) was performed, and a fasting blood sample was collected for other biochemical tests. Total body fat content was measured by the gas dilution method using a specific analyzer (Bod Pod; Life Measurement Inc., Concord, CA). IMCL in the right tibialis anterior muscle and IHL of segment 6 of the liver were measured by ¹H-MRS as previously described (8). In addition, intraabdominal and sc fat in a region extending from 8 cm above to 8 cm below the fourth and fifth lumber interspace (16 slices of slice thickness 10 mm) were measured by magnetic resonance imaging (VISART EX V4.40; Toshiba, Tokyo, Japan) as previously described (10) (n = 8). On a separate day, peripheral insulin sensitivity and SGU were evaluated by the euglycemic hyperinsulinemic clamp using the oral glucose load (OGL) method as previously described (11) (n = 8). Briefly, with the use of artificial endocrine pancreas (STG22; Nikkiso, Shizuoka, Japan), euglycemic-hyperinsulinemic clamp (target plasma glucose of 95 mg/dl and insulin infusion rate of 100 mU/m²·min) was applied, and the mean glucose infusion rate (GIR) from 105–120 min after insulin infusion was used as a marker of peripheral insulin sensitivity. Then, glucose was administered orally at a dose of 0.5 g/kg body weight, and GIR was diminished to maintain a euglycemic condition for 180 min. SGU was calculated as described previously (11). Briefly, total amount of SGU was calculated from the difference between the amount of ingested glucose and the summation of GIR decrements after glucose ingestion. Then, SGU was expressed as the percentage of ingested glucose amount. The accuracy of SGU measurement has been well discussed in previous reports (11, 12, 13, 14).

In addition, a well-trained dietician calculated total energy intake and diet composition from 3-d food diaries. Mean physical activity level for 3 months was estimated with an ambulatory accelerometer (Lifecorder; Suzuken, Nagoya, Japan) (8). Then, all subjects were instructed to consume a nutritionally balanced diet (35 kcal/kg ideal body weight) that consisted of about 25% of energy as fat, about 60% as carbohydrate, and about 15% as protein by the dietitian. All subjects used formula diet Obecure (USCure Inc., Tokyo, Japan) once a day, as an adjunct to the nutritionally balanced diet. All subjects were instructed to visit our hospital every week and were encouraged to maintain calorie restriction by the dietician.

Even after completion of the 3-month calorie restriction period, four subjects failed to achieve 5–10% body weight reduction. Thus, in this study, we excluded these four subjects from this study. In the remaining 13 patients, we reevaluated all the parameters described above after the 3-month calorie restriction period.

Statistical analysis

All data are expressed as the mean ± SD. Baseline data were compared with those obtained after treatment by the paired t test. Simple linear regression analysis was performed to evaluate metabolic parameters. Statistical significance was set at P < 0.05.

	Results

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Metabolic parameters

Table 1 shows the clinical characteristics of 13 study subjects before and 3 months after the treatment. The weight loss regimen involved 522 kcal/d calorie reduction during the 3-month period. Although protein intake did not change during the period, carbohydrate (from 1456 ± 296 to 1156 ± 202 kcal, P < 0.01) and fat consumption (from 860 ± 144 to 637 ± 137 kcal, P < 0.01) was significantly decreased. On the other hand, no significant change in daily physical activity was observed. Thus, the moderate weight reduction observed in our subjects was mainly achieved by calorie restriction of carbohydrate and fat. The weight loss regimen resulted in a significant but only 6% fall in body weight in 3 months. Although the mean BMI value was still above 30 kg/m² and the mean waist circumstance was also markedly higher than the limit of metabolic syndrome (85 cm) for Japanese men, diastolic blood pressure decreased significantly during the period. In addition, the weight loss regimen resulted in significant improvement of fasting plasma insulin, HOMA-IR, glycated hemoglobin, serum low-density lipoprotein-cholesterol, and triglyceride but no significant increase in serum adiponectin. Both the areas under the curve of plasma glucose and insulin during OGTT were significantly decreased after the weight reduction program (Table 1).

The steady-state insulin levels were comparable between the pre- and posttreatment period at 120 min (pre, 266.6 ± 75.5 µU/ml; post, 250.1 ± 35.4 µU/ml) and 300 min (pre, 241.7 ± 86.5 µU/ml; post, 272.9 ± 50.3 µU/ml) during the clamp study. The steady-state GIR before OGL, mainly reflecting glucose uptake in skeletal muscle, was not significantly improved by the diet therapy (from 5.63 ± 1.06 to 6.39 ± 1.23 mg/kg·min, P = 0.22; Fig. 1A). SGU was significantly increased from 13.5 ± 20.0 to 35.0 ± 30.8% (P = 0.023; Fig. 1B). This metabolic change in the liver was associated with a 36% reduction of IHL (from 12.9 ± 6.2 to 8.2 ± 4.6%, P = 0.023; Fig. 1D). On the other hand, no significant change was observed in IMCL (from 2.95 ± 1.29 to 3.11 ± 1.71, P = 0.70), similar to GIR (Fig. 1C).

View larger version (13K): [in this window] [in a new window]   FIG. 1. The changes of glucose uptake and intracellular lipids in muscle and liver by caloric restriction. A and B, GIR (A) and SGU were evaluated by euglycemic-hyperinsulinemic clamp with OGL before and after calorie restriction program (n = 8); C and D, IMCL (C) and IHL (D) were measured by 1H-MRS before and after calorie restriction program. IMCL was quantified by methylene signal intensity (S-fat) at approximately 1.25 ppm and the creatine signal at 3.0 ppm (Cre) as the reference, and calculated as a ratio relative to Cre (S-fat/Cre). IHL was quantified by S-fat and H2O at about 4.7 ppm as the internal reference and calculated as a percentage of H2O + S-fat [S-fat x 100/(H2O + S-fat)] (n = 13). E, Correlation between rate of reduction of IHL and that of visceral fat volume. Changes in IHL correlated significantly with the percent change in visceral fat content (r = 0.823; P < 0.01; n = 8).

As shown in Table 1, total body fat, visceral fat, and abdominal sc fat each significantly decreased after the weight reduction program. Although the rate of reduction of IHL did not correlate with that of total fat mass (r = 0.334; P = 0.27) or abdominal sc fat (r = 0.519; P = 0.20), it correlated significantly with the rate of reduction of visceral fat (r = 0.823; P < 0.01) (Fig. 1E).

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
The present study evaluated the effects of moderate weight loss by calorie restriction for 3 months in nondiabetic obese male subjects. The moderate weight reduction resulted in reduction of body fat and IHL but not IMCL. This change coincided with an increase in SGU but not in peripheral insulin sensitivity. In addition, the reduction in IHL correlated closely with reduction in visceral fat but not sc fat.

Recently, Petersen et al. (9) showed that 8% weight reduction by a moderately hypocaloric very-low-fat diet within 7 wk results in 80% reduction of IHL in type 2 diabetes, and this reduction was associated with improvement in hepatic insulin resistance. In the present study, moderate weight loss resulted in reduction of IHL, which was associated with an increase in SGU. Our data, together with those of others (9), demonstrate that moderate weight loss by calorie restriction can improve glucose metabolism in the liver with reduction of hepatic fat accumulation.

We reported previously that a 2-wk diet plus exercise therapy in hospitalized type 2 diabetes patients resulted in 19% reduction of IMCL and 56% increase in peripheral insulin sensitivity (8). These changes were not observed in patients on diet restriction but no exercise therapy (8). With regard to these findings, Petersen et al. (9) did not observe any changes in IMCL and peripheral insulin sensitivity by a 7-wk program of a moderately hypocaloric very-low-fat diet (3%). Furthermore, in the present study, no significant changes in physical activity, IMCL, and GIR were observed. Thus, increased physical activity by exercise therapy seems to be needed to reduce IMCL and improve insulin resistance in muscle.

In the present study, restriction of fat intake was estimated as approximately 220 kcal/d. A previous study revealed that about 15% of liver fat content was accounted for by dietary fat in nonalcoholic fatty liver patients (15). In addition, several studies showed that dietary fat intake was closely associated with IHL (8) (10, 16). On the other hand, several studies described a link among visceral fat mass, hepatic free fatty acid (FFA) load, and hepatic fat accumulation (16, 17, 18). The present study also showed a significant correlation between the percent reduction in visceral fat volume and that in IHL. Although we did not directly measure the FFA kinetics, this result suggests that reduction of hepatic FFA load originating from dietary fat and visceral fat may be involved in the reduction of IHL seen in the present study.

With the decrease in IHL by moderate weight loss, SGU, which at least in part reflects hepatic glucose uptake (12), was significantly increased in the present study. Similarly, our previous study showed improvement in SGU after 2 wk of diet therapy with or without exercise therapy, which was associated with IHL reduction (8). Bajaj et al. (14) also demonstrated that pioglitazone treatment decreased IHL and increased SGU. These results suggest the presence of a tight link between reductions in IHL and rises in SGU. Impairment of SGU could be due to one or more of the following mechanisms: poor glycemic control (13, 14) and lower glucokinase activity (19). However, the exact mechanism that explains the link between IHL and SGU remains unclear.

In this study, estimation of SGU is based on the assumption that endogenous glucose production (EGP) is suppressed during the clamp study and not changed after OGL. However, we cannot exclude the possibility that EGP after OGL might be affected by dietary intervention. Regarding these concerns, EGP level should be theoretically suppressed under a hyperinsulinemic state. In addition, previous reports described that glucagon level was decreased during euglycemic-hyperinsulinemic clamp and not changed after OGL in any metabolic states (12, 20). Although we should take the study limitation into consideration, as previously described, we can reasonably estimate SGU using this method.

Recently, the importance of metabolic syndrome as a risk factor for the onset of cardiovascular disease and progression of type 2 diabetes has been emphasized (1). Our data suggest that moderate weight loss (5–10%) resulted in reduction of IHL, which in turn resulted in improvement of SGU. This metabolic change in the liver might explain the beneficial effect of moderate weight reduction in the prevention of cardiovascular disease.

	Acknowledgments

 
We thank the trainers (K. Kawakami and T. Ohnishi), dietician (M. Shinomiya), and nurses for their management of lifestyle modification at the Sports Clinic in Juntendo University Hospital. We also thank J. Makita, M. Umeda, and M. Hirayama for MRS analysis.

	Footnotes

 
Disclosure Statement: The authors have nothing to disclose.

First Published Online May 22, 2007

Abbreviations: EGP, Endogenous glucose production; FFA, free fatty acid; GIR, glucose infusion rate; ¹H-MRS, ¹H-magnetic resonance spectroscopy; IHL, intrahepatic lipid; IMCL, intramyocellular lipid; OGL, oral glucose load; OGTT, oral glucose tolerance test; SGU, splanchnic glucose uptake.

Received October 31, 2006.

Accepted May 14, 2007.

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