Aromatic amino acids in the brain function as precursors for the monoamine neurotransmitters serotonin (substrate tryptophan) and the catecholamines [dopamine, norepinephrine, epinephrine; substrate tyrosine (Tyr)]. Unlike almost all other neurotransmitter biosynthetic pathways, the rates of synthesis of serotonin and catecholamines in the brain are sensitive to local substrate concentrations, particularly in the ranges normally found in vivo. As a consequence, physiologic factors that influence brain pools of these amino acids, notably diet, influence their rates of conversion to neurotransmitter products, with functional consequences. This review focuses on Tyr and phenylalanine (Phe). Elevating brain Tyr concentrations stimulates catecholamine production, an effect exclusive to actively firing neurons. Increasing the amount of protein ingested, acutely (single meal) or chronically (intake over several days), raises brain Tyr concentrations and stimulates catecholamine synthesis. Phe, like Tyr, is a substrate for Tyr hydroxylase, the enzyme catalyzing the rate-limiting step in catecholamine synthesis. Tyr is the preferred substrate; consequently, unless Tyr concentrations are abnormally low, variations in Phe concentration do not affect catecholamine synthesis. Unlike Tyr, Phe does not demonstrate substrate inhibition. Hence, high concentrations of Phe do not inhibit catecholamine synthesis and probably are not responsible for the low production of catecholamines in subjects with phenylketonuria. Whereas neuronal catecholamine release varies directly with Tyr-induced changes in catecholamine synthesis, and brain functions linked pharmacologically to catecholamine neurons are predictably altered, the physiologic functions that utilize the link between Tyr supply and catecholamine synthesis/release are presently unknown. An attractive candidate is the passive monitoring of protein intake to influence protein-seeking behavior.

Little is known about the effects on the skeleton of laparoscopic Roux-en-Y gastric bypass (LRGB) surgery for morbid obesity and subsequent weight loss. We compared 25 patients who had undergone LRGB 11 +/- 3 months previously with 30 obese controls matched for age, gender, and menopausal status. Compared with obese controls, patients post LRGB had significantly lower weight (92 +/- 16 vs. 133 +/- 20 kg; P < 0.001) and body mass index (31 +/- 5 vs. 48 +/- 7 kg/m(2); P < 0.001). Markers of bone turnover were significantly elevated in patients post LRGB compared with controls (urinary N-telopeptide cross-linked collagen type 1, 93 +/- 38 vs. 24 +/- 11 nmol bone collagen equivalents per mmol creatinine; and osteocalcin, 11.6 +/- 3.4 vs. 7.6 +/- 3.6 ng/ml; both P < 0.001). Fifteen patients were studied prospectively for an average of 9 months after LRGB. They lost 37 +/- 9 kg and had a 29 +/- 8% fall in body mass index (both P < 0.001). Urinary N-telopeptide cross-linked collagen type 1 increased by 174 +/- 168% at 3 months (P < 0.01) and 319 +/- 187% at 9 months (P < 0.01). Bone mineral density decreased significantly at the total hip (7.8 +/- 4.8%; P < 0.001), trochanter (9.3 +/- 5.7%; P < 0.001), and total body (1.6 +/- 2.0%; P < 0.05), with significant decreases in bone mineral content at these sites. In summary, within 3 to 9 months after LRGB, morbidly obese patients have an increase in bone resorption associated with a decrease in bone mass. Additional studies are needed to examine these findings over the longer term.

Obesity. 2006;14:1626 -1636. Objective: Because post-bariatric surgery patients undergo massive weight loss, the resulting skin excess can lead to both functional problems and profound dissatisfaction with appearance. Correcting skin excess could improve all these corollaries, including body image. Presently, few data are available documenting body image and weight-related quality of life in this population. Research Methods and Procedures:Eighteen patients who underwent both bariatric surgery and body contouring completed our study. Both established surveys and new surveys designed specifically for the study were used to assess body perception and ideals, quality of life, and mood. Patients were surveyed at the following time-points: pre-body contouring (after massive weight loss) and both 3 and 6 month post-body contouring. Statistical testing was performed using Student's t test and ANOVA. Results: The mean age of the patients was 46 Ϯ 10 years (standard deviation). Quality of life improved after obesity surgery and was significantly enhanced after body contouring. Three months after body contouring, subjects ascribed thinner silhouettes to both current appearance and ideal body image. Body image also improved with body contouring surgery. Mood remained stable over 6 months.Discussion: Body contouring after surgical weight loss improved both quality-of-life measurements and body image. Initial body dissatisfaction did not correlate with mood. Body contouring improved body image but produced dissatisfaction with other parts of the body, suggesting that as patients become closer to their ideal, these ideals may shift. We further developed several new assessment methods that may prove useful in understanding these post-surgical weight loss patients.

Persistent serotonergic and behavioral abnormalities after recovery raise the possibility that these psychobiological alterations might be trait-related and contribute to the pathogenesis of BN.