One moderate quality study(1) examined the effectiveness of a two-week protein-rich hypocaloric diet (protein= 75 g/day; kcal= 913 kcal/day) compared to a standard hypocaloric diet (protein= 58 g/day; kcal= 841 kcal/day) in patients awaiting bariatric surgery.
The study compared the BCM Diat™ diet to a control diet (Optifast™). Both diets included a combination of soups and shakes, and the BCM Diat™ diet also included flavoured bars. Participants in both groups were also allowed to consume 200g/day low starch vegetables, and calorie-free beverages.
The evidence of effectiveness of two-week hypocaloric protein-rich diet interventions is lacking for the following outcomes:
Weight outcomes:
Might not be effective (one moderate quality study; no significant difference between the two diet groups for weight reduction, excess weight loss, BMI or body circumference measures)(1).
Liver volume:
Might not be effective (one moderate quality study, no significant difference between the two diet groups)(1).
Liver fat content:
Might not be effective (one moderate quality study, no significant difference between the two diet groups)(1).
MRI Visceral adipose tissue mass:
Might not be effective (one moderate quality study, no significant difference between the two diet groups)(1).
Changes in serum parameters:
Might not be effective (one moderate quality study, no significant difference between the two diet groups for LDL & HDL cholesterol and triglycerides, fasting glucose,HbAc1, c-reactive protein, ALAT, ASAT, Haemoglobin, Haematocrit, thrombocytes and erythrocytes)(1).
Adverse events:
No serious adverse events were observed during the study(1).
Evidence Service comments:
It is worth mentioning that when the results from both diets were pooled and analysed together, the authors did identify that very low-calorie diets in general may be effective for improving several of the above outcomes. However, as shown above, they did not find that the BCM Diat™ Diet was statistically better than the Optifast™ diet for any outcome(1).
This study took place in Germany(1), thus generalisability to the Welsh context needs to be considered.
The intervention took place in patients waiting for bariatric surgery and therefore may not be applicable to patients waiting for other elective surgeries.
It is suggested that further robust research and thorough evaluation of impact is needed.