Adults with severe obesity cut their daily calorie intake significantly during the first year regardless of whether they underwent bariatric surgery or followed a structured diet program, according to a prospective cohort study published online in Obesity. However, eating habits diverged after that initial period, with energy intake remaining stable in surgery patients but climbing in the diet group.
How did calorie intake compare between surgery and diet groups over three years?
Reported energy intake fell by an average of 1,322 kJ per visit during the first year across all participants, with no significant differences in early reductions between the surgical and structured diet groups. Between 12 and 24 months, daily energy intake rose in the diet group by an average of 3,089 kJ per visit. By contrast, energy intake remained comparatively stable in groups that underwent laparoscopic adjustable gastric banding, sleeve gastrectomy, or Roux-en-Y gastric bypass.
What were the recorded body weight changes at three years?
Weight loss remained substantial among surgical patients tracked through the three-year mark ending in October 2015. At three years, body weight remained 25.1% below baseline after sleeve gastrectomy, 26.4% below baseline after Roux-en-Y gastric bypass, and 16.9% below baseline after laparoscopic adjustable gastric banding. The structured diet group was not assessed for body weight at the three-year interval.
How did appetite and physical activity shift after treatment?
Premeal appetite scores dropped from a median of six to two at every visit following sleeve gastrectomy. These appetite suppression effects were smaller after laparoscopic adjustable gastric banding, short-lived after Roux-en-Y gastric bypass, and absent in the diet group. Macronutrient shifts mostly faded within a year, but calcium intake increased after Roux-en-Y gastric bypass and sleeve gastrectomy, while moderate physical activity rose after Roux-en-Y gastric bypass.
How do short-term metabolic effects differ between surgery and low-energy diets?
In a separate randomized controlled trial, researchers investigated patients on a waiting list for obesity surgery randomized to either undergo surgery directly or follow a low-energy diet. One month after treatment initiation, both obesity surgery and the low-energy diet induced similar reductions in body weight, averaging 7.7 kg and 7.4 kg respectively, alongside a 7% reduction in adipose tissue volume and a 2% unit decrease in liver fat content.
Despite similar weight loss, only obesity surgery led to significant reductions in fasting plasma glucose and insulin resistance, alongside distinct changes in insulin-stimulated glucose fluxes to specific tissues. The homeostatic model assessment of insulin resistance dropped by 26.3% following surgery and non-significantly by 20.9% following the low-energy diet.
What do clinical guidelines recommend for long-term patient care?
The Obesity study was led by Michael Do at Blacktown Hospital in Sydney, Australia, with patient recruitment running from October 2009 through May 2012. Study authors noted that the findings reinforce current clinical guideline recommendations for lifelong, multidisciplinary follow-up. This ongoing care includes dietary counseling, nutritional supplementation, psychological support, and structured physical activity programs.
Frequently Asked Questions
What were the primary study limitations noted by the researchers?
Group assignment was not randomized and relied on patient and clinician preference, introducing potential selection bias and confounding. Additionally, dietary intake and physical activity were self-reported, and small group sizes—particularly for the Roux-en-Y gastric bypass cohort—alongside participant dropout, may have reduced estimate precision.
Which funding sources and disclosures were reported for the trials?
The Obesity study received support from a National Health and Medical Research Council Scholarship, with two authors reporting honoraria, advisory board roles, consulting fees, or research support from pharmaceutical companies. The trial published in Diabetologia was funded by grants including AstraZeneca R&D, the Swedish Diabetes Foundation, the European Union’s Horizon Europe Research project PAS GRAS, the European Commission, EXODIAB, the Family Ernfors Foundation, the P.O. Zetterling Foundation, Novo Nordisk Foundation, the Agnes and Mac Rudberg Foundation and the Uppsala University Hospital ALF grants under clinical trial registration NCT02988011.
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