Mozaffar, Boshra
(2024)
The impact of zinc levels on taste change and hair loss following bariatric surgery and reporting of dietary compliance to weight loss interventions.
PhD thesis, University of Nottingham.
Abstract
Currently, there is significant interest in the effective treatment of obesity, particularly the implementation of a very low-calorie diet (VLCD) and the use of bariatric surgery (BS) which is a well-established long-term treatment. However, much of the contemporary research has noted that patients who have undergone bariatric surgery have reported unexplained side effects, such as a change in their sense of taste which may impact dietary compliance post-surgery. Additionally, there is limited research concerning long-term compliance with a very low-calorie diet which is a crucial aspect of pre-and post-bariatric surgery eating requirement. This thesis is divided into two sections: the first section investigates the links between taste change and zinc following BS, and the second section examines patients’ compliance with a VLCD. The over-arching theme of the thesis focuses on the speculative association of taste and hair loss following bariatric surgery with decreased circulating zinc levels, which might affect compliance to post-surgery eating requirements and the reporting of compliance to significant calorie restriction. In the initial part of the first section, a systematic review was conducted to collect evidence regarding the role of zinc in the development of taste disorders among patients who had undergone bariatric surgery and those who had not. This study used PRISMA guidelines to conduct systematic reviews of several electronic bibliographical databases, including EMBASE, PubMed, AMED, and MEDLINE, for studies concerning the effects of BS on taste, the effects of BS on zinc levels, and the effect of zinc replacement on taste. The results from this systematic review demonstrated that, according to the findings of qualitative research (conducted via questionnaires), taste change was observed in the majority of patients within a year following bariatric surgery. However, experimental investigations did not yield statistically significant evidence of taste alteration. A total of twelve investigations were conducted to examine the occurrence of zinc deficiency following bariatric surgery (BS), which revealed a notable reduction in zinc levels that persisted for six months post-surgery. The administration of zinc sulphate was found to be efficacious in enhancing taste perception in patients, apart from those with a cancer diagnosis who did not exhibit any improvement in taste following the dispensation of zinc supplements.
Given that zinc deficiency and taste disorders occur in repeated cases at approximately the same time, this study hypothesises the existence of a potential relationship between these two factors. Therefore, the subsequent section of this work examines the connection between zinc and taste change following sleeve gastrectomy (SG) and gastric bypass (GB) via a single-centre, prospective cohort study conducted at King Abdullah Medical City (KAMC) in Saudi Arabia (Makkah). Forty-three patients were selected, consisting of eighteen gastric bypass patients and twenty-five patients who had undergone sleeve gastrectomy (SG). The duration of the follow-up period spanned a length of six months. The assessment of taste alteration was conducted via the utilisation of a validated questionnaire and implementation of the taste strips technique. Additionally, the study involved the measurement of serum zinc levels and salivary flow rate for all of the participants.
Following the administration of the questionnaire, the results of this study demonstrate that patients who had undergone gastric bypass (GB) surgery exhibited a higher prevalence of hypogeusia (at the three-month mark) when compared with those who underwent sleeve gastrectomy (SG), with percentages of 72.0% and 36.0% respectively (p=0.03). However, no significant difference in hypogeusia prevalence was discovered between the two groups at the six-month mark, with percentages of 56.0% for GB and 45.0% for SG patients (p=0.74). However, when taste strips were utilised, there was no notable disparity in the occurrence of hypogeusia between patients with GB and SG at the three-month point (44.4% versus 36.0%, p=0.75). Nevertheless, at six months, a higher proportion of patients with GB reported experiencing hypogeusia compared to SG patients (44.0% vs. 11.0%, p=0.052). The study observed a significant decrease in zinc levels among GB patients, from the initial measurement of 85.6±16.9μgm /dl to the six-month measurement of 67.5±9.2μgm/dl. Conversely, SG patients reported an increase in zinc levels from the baseline measurement of 76.9±11.4 to the six-month measurement of 84.9±21.7μgm/dl. A decrease in the salivary flow rate was noted in 66.0% and 72.0% of individuals with GB and SG, respectively, after 3 months, and in 47.0% and 70.0%, respectively, after 6 months.
Hair loss was noted as an additional side-effect following BS; however, the underlying causes and factors of this condition remain unidentified. Therefore, a subsequent section investigates the potential association between hair loss and decreased circulating zinc levels following BS and the differences between SG and GB patients. The findings of the study revealed that the prevalence of hair loss among patients who underwent GB was double that of SG. Specifically, at three months post-surgery, the percentage of hair loss was 66.6% in the GB group and 32% in the SG group, indicating a significant difference between the two groups (P = 0.025). Furthermore, at six months post-surgery, the percentage of hair loss increased to 75% among GB patients, while it decreased to 20% among SG patients. The findings also indicated a statistically significant difference between the groups, with a p-value of 0.001. This research established that individuals who had undergone bariatric surgery and experienced subsequent hair loss displayed reduced zinc levels compared to the established reference value and that, in this patient population, females were more susceptible to hair loss than males.
These findings suggest that hair loss is a frequently observed adverse outcome that can occur following both types of surgeries; however, it has been shown that GB patients are inclined to experience a higher degree of hair loss, which has been linked to lower levels of zinc in their blood.
In the final part of this section, a study assessed the effective zinc doses for taste disorder treatment to inform future clinical guidelines and studies regarding the use of zinc as a remedy for taste disorders following BS. A systematic review and meta-analysis were conducted regarding the effectiveness of zinc supplementation in taste disorder treatment following the guidelines outlined in the PRISMA Statement. A comprehensive search of four electronic bibliographic databases (Ovid MEDLINE, Ovid Embase, Ovid AMAD, and PubMed) was conducted. This review has been duly recorded with PROSPERO and assigned the unique identification number CRD42021228461. The results demonstrate that zinc supplementation, when administered at high dosages ranging from 68 to 86.7 mg/d for a duration of up to six months, is an efficacious intervention for taste abnormalities in individuals with zinc deficiency, idiopathic taste disorders, and those with taste disorders resulting from chronic renal failure.
The second section of this thesis concerns a clinical study involving thirty-five, healthy, middle-aged male volunteers and is designed to investigate and document the consumption of an extra calorie allowance derived from conventional foods or only from vegetables and nuts (up to 200kcal/day). Additionally, this study employed two distinct evaluation methodologies to analyse the macronutrient composition of these dietary additions to evaluate VLCD compliance for up to six weeks. The results revealed that patients following a very low-calorie diet (VLCD) who are provided with an additional food allowance from traditional sources or have their food intake confined to vegetables and nuts, frequently consume more calories than the prescribed daily limit. How compliance is reported exhibits substantial variation depending on the method of monitoring employed.
The data presented in the conclusion of this thesis suggest that: firstly, decreased circulating zinc level following bariatric surgery is directly correlated to taste change, low salivary flow and hair loss, and that high doses of zinc supplementation are an effective remedy for taste change; and, secondly, patients fail to strictly adhere to VLCD. Additionally, the data presented by this thesis suggests that future research concerning the effectiveness of zinc supplementation in taste disorder treatment (following bariatric surgery), and additional studies concerning long-term compliance with a very low-calorie diet, are required.
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