Preoperative weight loss is often suggested as a means of reducing operative risk in obese patients requiring laparotomy but there are no large studies documenting that this is feasible or helpful. Although several commercial products are available that provide high levels of protein with low levels of carbohydrates in convenient liquid preparations, recommendations regarding the extent to which weight loss can be pursued preoperatively are not available.

To determine whether it is practical and safe to have obese patients lose weight pre-operatively.

We asked 100 severely obese patients requesting gastric bypass surgery to diet before their operations. Seventy patients agreed to diet by consuming a 420 Kcal, 70 g protein liquid diet daily for at least 1 month.

Forty-seven patients lost at least 7.5 kg (mean ± SD 17.1 ± 0.7). The patients who successfully lost weight preoperatively (dieters group) were significantly heavier than patients (nondieters group) who did not lose weight (251% ± 45% of ideal body weight [IBW]versus 229% ± 33% IBW, respectively; P <0.01), had a significantly higher ratio of men to women, and had psychiatric evaluations and psychological test scores that suggested significantly more psychopathology. Other biosocial and medical characteristics were similar. Postoperatively, the dieters and nondieters had similar rates for morbidity. Dieters and nondieters had no differences in wound-healing complications, and subgroups who had collagen deposition measured experimentally had similar amounts of hydroxyproline accumulation in their wounds.

These results suggest that a preoperative diet program appeals more to certain subgroups of severely obese patients than to others. An aggressive preoperative weight loss program that encourages patients to lose an average of 17 kg is safe and can be accomplished practically using available commercial products.