Background: Discussion has continued concerning calorie restriction (CR) and low carbohydrate diet (LCD). LCD was developed by Bernstein, Atkins and others, and by our co-authors in Japan. In this study, we report and discuss long-term effects in 2,699 cases, and short-term effects and hyperketonemia in 51 cases. Subjects and Methods: Study 1 (long-term): Subjects were 2,699 cases with diabetes, metabolic syndrome, or both. Methods included continuing LCD and measuring weight reduction in six to twelve months. Study 2 (short-term): Twenty-four diabetics were compared on a CR diet (1,400 kcal/day, carbo-60%) and a super-LCD (1,400 kcal/day, carbo-12%). We recently tried insulinogenic index-carbo70 (IGI-carbo70) from glucose and immunoreactive insulin (IRI; 0, 30 min) for a meal of carbohydrates of 70 g. Study 3 (hyperketonemia): Blood ketone bodies and 3-hydroxybutylic acid (3-OHBA) were measured in 51 diabetics with super-LCDs. Results: Study 1: Weight reduction of more than 10% was observed in 25.6% of subjects, and more than 2.5% was observed in 78.8% of subjects. Study 2: Base data included HbA1c 7.7 ± 1.4 %, homeostasis model assessment (HOMA)-R 3.2 ± 1.9, and HOMA-β 44.5 ± 37.0. Responses of blood glucose to meals (0-120 min) were 156 → 236 mg/dL to CR and 116 → 141 mg/dL to LCD for ten days. Triglyceride value decreased from 143.4 ± 86.8 mg/dL to 93.9 ± 34.8 mg/dL on LCD for ten days. IGI-carbo70 showed less than 0.5 in 75% of cases. Study3: Total ketone bodies were measured in four groups, which were A (4 to 5 days), B (7 to 9 days), C (11 to 13 days), D (21 to 28 days), with an average value of 994 μmol/mL in C, 36 to 623 μmol/mL in A, B, and D. As 3-OHBA value increases from normal (<85 μmol/mL) to extremely high (3,577 μmol/mL), the ratio increases from 60% - 70% up to 90%. Conclusion: Long-term effects of LCD would be successful. Short-term effects revealed that the change from CR to LCD in only ten days caused a significant decrease of blood glucose and triglycerides. Similar to the 75 g oral glucose tolerance test (OGTT), intake of a meal with carbohydrates of 70 g would be clinically simple and useful as insulinogenic index (IGI)-carbo70. Super-LCD would increase blood ketone bodies about three fold of the standard level in four to five days. These findings would be the fundamental data in the LCD area and contribute the research of glycative changes.