HIGHER FIBRE HIGHER CARBOHYDRATE VS. LOWER FIBRE LOWER CARB. DIETS FOR DIABETES MANAGEMENT

By the end of the 20th Century, research was indicating that lower fat, higher carbohydrate diets had not brought all of the anticipated benefits, in part because people had been consuming more refined available carbohydrates (i.e., maltodextrins, starches and sugars), but not more dietary fibre. So lower carbohydrate, higher fat diets were once again promoted by some individuals and organisations.

A quarter of a century later, the debate about higher versus lower carbohydrate diets for people with diabetes continues.

As mentioned in this month’s Food for Thought, because dietary fibre comes predominantly from plant foods, higher carbohydrate diets are in general higher in fibre and vice versa, lower carbohydrate diets are lower in fibre, without very careful meal planning and/or use of fibre supplements.
For example, here in Australia, total available carbohydrate consumption has been decreasing (225.9g per day in 2011-12 vs. 208.3 g per day in 2023) and so has fibre (22.9g per day in 2011-12 vs. 20.7 g per day in 2023).

A new systematic review and meta-analysis of randomised controlled trials (RCTs) has examined the evidence for the effect of higher fibre and higher carbohydrate diets compared to lower fibre and lower carbohydrate diets in people with diabetes.

Through comprehensive scientific literature searches, 10 RCTs lasting at least 6 weeks were identified, including a total of 499 people with diabetes (9 with type 1 and 490 with type 2). Diets classified as higher fibre/higher carbohydrate needed to differ from the diet in the lower fibre/lower carbohydrate arm by a minimum 5% in total energy (TE) intake derived from carbohydrates, and had to have a concomitant difference in dietary fibre intake of at least 3.5 g per day per 5%TE carbohydrate difference.

When compared to lower fibre/lower carbohydrate diets, higher fibre/higher carbohydrate diets reduced:

• HbA1c (glycated haemoglobin) by -0.50%
• fasting insulin by -0.99 μIU/mL
• total cholesterol by -0.16 mmol/L, and
• LDL (low-density lipoprotein) cholesterol by -0.16 mmol/L.

Importantly, trials with larger differences in fibre and carbohydrate intakes between interventions reported greater reductions in these important risk factors.

The authors concluded that the new analyses, alongside existing evidence and guidelines, indicate that nutrition guidance should not focus on carbohydrate amount, but carbohydrate type and source (i.e., quality) instead. Dietary fibre intakes for adults with diabetes should be at least 35 g per day, through the intake of minimally processed carbohydrate-containing foods including whole grains, legumes, vegetables, and fruit.

In support of this conclusion, Diabetes organisations are advising health professionals and people with diabetes to focus more on foods rather than get caught up in endless debates about macronutrients.

• Barclay. Reversing Diabetes. Murdoch Books, 2015.
• Reynolds and colleagues. Higher fiber higher carbohydrate diets better than lower carbohydrate lower fiber diets for diabetes management. Obes Rev. 2025.
• American Diabetes Association. 5. Facilitating Positive Health Behaviors and Well-being to Improve Health Outcomes: Standards of Care in Diabetes—2026. Diabetes Care, 2026.