**2. Methods**

*New Insights into Metabolic Syndrome*

constant caloric intake across days [3].

have been studied well (Review [10]).

people using low-carbohydrate-high protein diet.

highly processed foods [1, 4].

index unless overtaken.

drate diet.

sis after exercise.

and glutamine decreased [17].

The presence of signals about energetic value of food between gut and brain was proposed by experiments in which rodents were given isocaloric diets that varied in volume and rodents accurately took the volume of food consumed to maintain

The volumes and contents of foods we take will be conveyed to the brain by a gut-brain circuit [4], and it is proposed that intake of highly processed foods disturbs the circuitry resulting in the confusion of the processing of foods information in the brain. This may be the reason of overeating and obesity by the intakes of

We recently gave sucrose or glucose to healthy men and measured changes in plasma levels of various amino acids [5] and changes in body mass index [6]. We now review the results and discuss roles of sugar in maintaining plasma levels of amino acids. We also report that sugar intake did not result in increase in body mass

Many researchers paid attention to the central control of appetite and gut motor

and hormonal functions [7–9]. Many studies have been performed on roles of tryptophan and leucine in the regulation of food intake and appetite [7–9]. Since serotonin is derived from tryptophan roles of serotonin in the regulation of appetite

Since intakes of carbohydrates considered to increase the release of insulin, which increase fat deposition, thus obesity, low carbohydrate diet has been popular in Japan lately. According to Noto et al. [11], high mortality rate was shown among

Robert Atkins first proposed that intakes of meat may result decrease of fat, thus prevent obesity. He died by a serious head injury when he toppled down [12], the impaired muscle functions has been suspected for the results of low carbohy-

The ability of insulin to stimulate glucose uptake and to suppress protein degradation in skeletal muscle is increased after exercise. Decrease in amino acid availability may prevent the stimulatory effect of insulin on muscle protein synthe-

Insulin is considered to regulate the metabolism of carbohydrate, lipid, protein, and amino acids [13]. Insulin inhibits protein degradation and the release of amino acids, and stimulates protein synthesis and amino acids uptake in skeletal muscles [14, 15]. When insulin levels were high, protein synthesis was stimulated in skeletal muscles [16]. In hyperglycemia plasma levels of alanine, phenylalanine, valine, leucine, isoleucine and tyrosine were shown to increase and the levels of histidine

It is shown that when plasma levels of tryptophan were raised by taking tryptophan in foods or by injection of insulin, serotonin and tryptophan in the brain increased [18, 19]. It is also shown that intake of carbohydrate resulted in secretion of insulin, which increased plasma levels of tryptophan and lowered the plasma levels of competing amino acids such as branched neutral amino acids in rats [19]. Carbohydrate intake was shown to decrease plasma levels of free amino acids and glucose intake resulted in a decrease in large neutral amino acids such as methionine, phenylalanine, tyrosine, and tryptophan [20, 21]. Possibly plasma glucose and insulin may stimulate transporters of some amino acids of peripheral tissues, especially muscles, resulting in decrease in the concentration of such amino acids

We administered glucose or sucrose solution to young and old men and examined plasma levels of various amino acids. In the present review we report the results [22, 23], and propose possible mechanisms with regard to the regulation of

**42**

in plasma.

appetite.

We asked men older than 50 years old and men college students to participate in the experiments. We checked their health carefully and recruited them if there were no health problems such as diabetes, hypertension nor serious diseases experienced in the past. They did not smoke in the past. We also excluded people who took drugs for dyslipidemia, hyperglycemia, or hypertension.

Participants were randomly assigned to groups after fasting overnight. Depending on their group, each participant received a 550-mL solution containing 50 g of glucose or sucrose (or 500 mL water as a control). Either 50 g of glucose or sucrose was added and dissolved in each bottle containing 500 mL of water. Between 9:00 AM and 10:00 AM, blood was taken using a syringe, and participants were given either glucose or sucrose solution or water as a control. We measured blood glucose using a finger stick (TERUMO kit) before and 120 min after the administration of glucose or sucrose. Furthermore, other plasma factors were measured after plasma was separated from blood. Ethylenediaminetetraacetic acid (EDTA) was used as an anticoagulant.

Blood was centrifuged to obtain plasma. The amino acid and insulin levels were measured for backgrounds of these participants.

To know energy intakes of various foods we used BDHQ (brief-type self-administered diet history questionnaires). From these questionnaires, we calculated the intake of energy, carbohydrate, fat and protein.

The samples were analyzed by SRL, Inc. (Tokyo Japan) using the UF-Amino Station®, which is a liquid chromatography-mass spectrometry system with an automated pre-column derivatization for simultaneous determination of amino acids (Shimadzu Corporation, Kyoto, Japan). The original concept of this system was developed by Ajinomoto Co., Inc. (Tokyo Japan) as an automated method of analyzing major free amino acids in human plasma in the field of clinical chemistry.

The human plasma samples were cryopreserved with EDTANa2 before the analysis. The thawed samples were deproteinized with acetonitrile followed by the amino acid analysis. Pre-column derivatization in the UF-Amino Station was automatically performed using an automated sample injector with the regent APDSTAG® (Wako Pure Chemical Industries, Ltd., Osaka, Japan). Target free amino acids as derivatized compounds were separated under a reversed phase ultrahigh-performance liquid chromatography condition and determined by the liquid chromatograph mass spectrometer.

Insulin was measured by the CLEIA (chemiluminescent immunoassay) method.
