Abstract
In bariatric practice, a preoperative weight loss of at least 5% is recommended. However, the hypocaloric diets prescribed vary and no consensus exists. This study examined the efficacy of preoperative diets in achieving 5% weight loss. From a systematic literature search, eight randomised controlled trials (n = 862) were identified. Half of the trials used a "very-low-calorie diet" whilst the rest employed a "low-calorie diet". Only five diets achieved ≥ 5% weight loss over varying durations and energy intakes. By inference, compliance with a 700-1050 kcal (2929-4393kJ) diet, consisting of moderate carbohydrate, high protein and low/moderate fat, for 3weeks is likely to achieve 5% weight loss. A low-carbohydrate diet (< 20g/day) may achieve this target within a shorter duration. Additional research is required to validate these conclusions.
Highlights
Obesity is a major global health issue both in terms of its increasing trajectory and as one of the leading causes of morbidity and mortality [1,2,3,4,5]
It is challenging for surgeons to elevate the left lobe of a large or fatty liver [16,17], especially during laparoscopic Roux-en-y gastric bypass surgery (RYGB), thereby, increasing the risk of liver injury and intraoperative bleeding [18]
A striking feature about the literature in this area is an increase in the number of publications of RCTs since 2014, probably due to the growing recognition that preoperative weight loss may optimise some perioperative outcomes [30,32,33,51]
Summary
Obesity is a major global health issue both in terms of its increasing trajectory and as one of the leading causes of morbidity and mortality [1,2,3,4,5]. Losing at least 5%TWL has been recommended for the treatment of non-alcoholic fatty liver disease [25] This is compatible with the general consensus that, regardless of a scheduled bariatric surgery, a modest weight loss, defined as 5-10 %TWL, has benefits on existing comorbidities [25,26] such as ameliorating hyperglycaemia or cardiovascular risk factors which are associated with increased perioperative risks [27,28]. An observational study, involving one-third of the bariatric centres in the United Kingdom found extensive variability in the type of energy-restricted diets prescribed preoperatively [35]. Given this lack of consensus amongst bariatric professions, there is a need to systematically review the highest level of evidence to determine the magnitude, macronutrient composition and duration of energy-restricted diets that may optimally achieve a preoperative weight loss of at least 5%
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