Still, large, long-term studies have been lacking. "However, large, long-term studies are needed to confirm the health benefits and safety of low- and very low-carbohydrate diets," Denzer says.

25 years of registry data

To help fill this gap, Lennerz and Denzer, together with colleagues in Germany, drew on 25 years of data from a diabetes prospective follow-up registry. They examined the relationship between VLC diets, growth, and metabolic safety in children aged 1 to 17.

The study involved 45,569 children with type 1 diabetes — 55% of them male, with an average age of 10.3 years — whose carbohydrate intake had been recorded at least twice over a period of a year or more.

The researchers sorted the children's diets by carbohydrate content, measured as the percentage of estimated energy intake:

• Very low-carbohydrate (VLC): less than 10% of energy from carbohydrates — 219 children
• Low-carbohydrate (LC): 10% to under 26% — 4,837 children
• Standard or higher-carbohydrate (SC): 26% or more — 40,513 children

Average follow-up periods were 2.18, 2.40, and 3.67 years, respectively.

The team tracked height and weight — accounting for the fact that the children were still growing — along with blood sugar trajectories, insulin use, and rates of two severe metabolic complications: hypoglycemia (dangerously low blood sugar) and diabetic ketoacidosis.

What the analysis found

The analysis did not identify any safety concerns in the areas examined. There was no evidence that a VLC diet stunted growth, and VLC diets were not associated with severe hypoglycemia or diabetic ketoacidosis.

Lower carbohydrate intake was also linked to favorable changes. BMI increased less over time in children following VLC and LC diets than in those on standard diets, staying closer to levels associated with a healthier weight.

Two other key markers pointed in the same direction. HbA1c — a measure of average blood sugar over the past two to three months — was lower at the end of follow-up and rose more slowly in the VLC and LC groups. The dose of basal insulin, one of two types of insulin typically prescribed for type 1 diabetes, was also lower and increased less over time.

Most notably, IDAA1c — a measure of blood sugar levels that factors in how much insulin a person uses — was lower at the end of follow-up in children on VLC and LC diets.

"IDAA1c combines blood sugar levels with the amount of insulin a person needs," Lennerz explains. "A lower IDAA1c therefore means that better blood sugar control was achieved without simply using more insulin, strengthening the finding that VLC and LC diets were associated with both better glycemic control and lower insulin requirements."

Important caveats

The researchers adjusted their analyses for factors including sex, age, migration background, and diabetes duration. However, they cannot rule out residual confounding — the possibility that other unmeasured factors influenced the results. Diet was self-reported, which may also have affected the findings.

Because the study was observational, it can show associations but cannot prove that the diets caused the observed benefits.

"Reducing carbohydrate intake improved glycemic control while reducing insulin needs without negatively impacting growth or increasing the rate of acute diabetes complications," Lennerz concludes. "These results are very encouraging but remain observational in nature. Additional research is needed to confirm the findings and establish the ideal amount of carbohydrate intake to maximize benefits while avoiding adverse effects and promoting food variety."

Families considering a low-carbohydrate approach for a child with type 1 diabetes should discuss it with their diabetes care team before making changes.