• There is much debate surrounding various diets for the management of adulthood obesity  
• Naude et al. (Cochrane Database of Systematic Reviews, 2022) compared the effects of low-carbohydrate weight-reducing diets to weight-reducing diets with balanced ranges of carbohydrates in adults who are overweight or obese without and with type 2 diabetes mellitus (T2DM) 

• Systematic review and meta-analysis 
• Study inclusion criteria 
  • RCTs 
  • Adults who are overweight or obese, with or without T2DM, and with or without cardiovascular conditions or risk factors 
  • Studies needed to  
    • Compare low-carb weight-reducing diets to balanced-carb (45% to 65% of total energy) weight-reducing diets 
    • Have a weight-reducing phase of at least 2 weeks or longer 
    • Be explicitly implemented for the primary purpose of reducing weight, with or without advice to restrict energy intake 

• Study design 
  • Certainty of evidence was assessed using GRADE criteria  
  • Analyses were stratified by  
    • Participants with and without T2DM 
    • Diets with weight-reducing phases only and those with weight-reducing phases followed by weight-maintenance phases 
  • Primary outcomes were assessed at  
    • Short-term follow-up (3 to <12 months)  
    • Long-term follow-up (≥12 months)  
• Primary outcomes 
  • Change in body weight (kg) 
  • Number of participants per group with weight loss of at least 5% 

• 61 RCTs | 6925 total participants 
• Included studies 
  • All studies were conducted in high-income countries, except for 1 in China 
  • Most investigated low-carb diets (> 50 g to 150 g per day or < 45% of total energy; n = 42) 
  • Quality of evidence was assessed as moderate to very low across outcomes 
• Included trial participant characteristics 
  • Mean baseline weight: 95 (range 66 to 132) kg 
  • Participants with T2DM: 1807  
    • Participants with T2DM mean age: 57 (range 50 to 65) years 
    • Participants without T2DM mean age: 45 (range 22 to 62) years 
  • Most trials included people without baseline cardiovascular conditions, risk factors or events (36 trials out of 61) 
  • Mean baseline diastolic blood pressure (DBP) and low-density lipoprotein (LDL) cholesterol across trials were within normal ranges 

• Participants both with and without T2DM lost weight when following weight reducing phases of both diets at  
  • Short-term follow-up: range 12.2 to 0.33 kg 
  • Long-term follow-up: range 13.2 to 1.7 kg 

• Low-carb weight-reducing diets vs balanced-carbo weight-reducing diets, probably result in little to no difference in change in body weight  
  • Over three to 8.5 months 
    • Mean difference −1.07 kg, (95% CI, −1.55 to −0.59) 
    • 3286 participants, 37 RCTs; moderate-certainty evidence 
  • Over one to two years 
    • MD −0.93 kg (95% CI, −1.81 to −0.04) 
    • 1805 participants, 14 RCTs; moderate-certainty evidence 
• There was also probably little to no difference in change in DBP and LDL cholesterol over one to two years 
• The evidence is very uncertain about whether there is a difference in the number of participants per group with weight loss of at least 5% at one year 
  • Risk ratio (RR) 1.11 (95% CI, 0.94 to 1.31) 
  • 137 participants, 2 RCTs; very low-certainty evidence 

• Low-carb weight-reducing diets compared to balanced-carb weight-reducing diets probably result in little to no difference in change in body weight 
  • Over three to six months 
    • MD −1.26 kg (95% CI; −2.44 to −0.09) 
    • 1114 participants, 14 RCTs; moderate-certainty evidence 
  • Over one to two years 
    • MD −0.33 kg (95% CI, −2.13 to 1.46) 
    • 813 participants, 7 RCTs; moderate-certainty evidence 
• There was also probably little to no difference in change in DBP, HbA1c and LDL cholesterol over 1 to 2 years 
• The evidence is very uncertain about whether there is a difference in the number of participants per group with weight loss of at least 5% at one to two years 
  • RR 0.90 (95% CI, 0.68 to 1.20) 
  • 106 participants, 2 RCTs; very low-certainty evidence 

• Evidence on participant-reported adverse effects was limited, so no conclusions are presented 

• Low-carb weight-reducing diets are probably no better or worse at promoting weight loss in participants who are overweight or obese than are balanced-carb weight-reducing diets  
• Type 2 diabetes status did not have a significant effect on diet type success 
• The authors state

There is probably little to no difference in weight reduction and changes in cardiovascular risk factors up to two years’ follow-up, when overweight and obese participants without and with T2DM are randomised to either low-carbohydrate or balanced-carbohydrate weight-reducing diets 

Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk 

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