Low-Carb Diets for Diabetes Care

Mechanisms: Why Carbohydrate Restriction Supports Glycemic Control

The glycemic effects of carbohydrate restriction are primarily related to reducing the amount of dietary carbohydrate that contributes to postprandial glucose excursions. Lower carbohydrate intake generally reduces postprandial glucose exposure and may decrease prandial insulin requirements. When carbohydrate restriction is accompanied by reduced energy intake and intentional weight loss, additional improvements in hepatic and peripheral insulin sensitivity may occur.

These effects should not be attributed solely to reductions in circulating insulin. The relationships among carbohydrate intake, insulin secretion, energy balance, adiposity, and insulin resistance are complex. Improvements in glycemia associated with low-carbohydrate dietary patterns likely reflect several interacting mechanisms, including reduced postprandial glucose exposure, changes in total energy intake, intentional weight loss, alterations in hepatic glucose production, and improvements in insulin sensitivity.

The carbohydrate-insulin model, associated with the work of David Ludwig, MD, PhD, and colleagues, proposes that hormonal responses to dietary carbohydrate may influence fuel partitioning, hunger, energy expenditure, and adiposity. Although this model has contributed to scientific discussion about diet composition and metabolism, aspects of the model remain debated, and it should not be presented as an established explanation for obesity or for the clinical benefits of carbohydrate restriction. Clinical counseling should instead emphasize demonstrated outcomes and individualized responses rather than relying on a single proposed mechanistic model.

Very low-carbohydrate or ketogenic dietary patterns produce additional metabolic adaptations. As carbohydrate availability decreases, insulin secretion generally declines relative to glucagon activity, promoting lipolysis and hepatic ketogenesis. Circulating ketone bodies can then serve as an alternative energy source for several tissues, while hepatic gluconeogenesis continues to maintain glucose availability for tissues with ongoing glucose requirements. Nutritional ketosis is a physiologic adaptation and should be distinguished from diabetic ketoacidosis.

These metabolic changes have important implications for medication management. Substantial carbohydrate restriction may reduce glucose-lowering medication requirements, particularly for patients using insulin or insulin secretagogues, increasing the need for proactive medication review to reduce the risk of hypoglycemia. In addition, very low-carbohydrate or ketogenic dietary patterns used in combination with sodium-glucose cotransporter 2 (SGLT2) inhibitors may increase the risk of euglycemic diabetic ketoacidosis. Clinicians should therefore review glucose-lowering medications before patients initiate substantial carbohydrate restriction and provide appropriate medication adjustment, education, and ongoing monitoring.

Clinical Evidence for Carbohydrate Restriction in T2D

Randomized trials and systematic reviews support low-carbohydrate dietary patterns as one of several evidence-based nutrition strategies for adults with type 2 diabetes (T2D). A 2021 review published in Frontiers in Nutrition reported that low-carbohydrate approaches may improve glycemic outcomes and reduce requirements for glucose-lowering medications in some patients.[6] However, interpretation of the evidence is complicated by substantial variation in how low-carbohydrate diets are defined, the intensity of dietary interventions, medication-adjustment protocols, comparator diets, adherence, and duration of follow-up.

Available trials have not consistently demonstrated greater cardiovascular risk with appropriately planned low-carbohydrate diets compared with other dietary approaches. However, long-term cardiovascular outcome data remain limited, and the cardiometabolic effects of a low-carbohydrate diet may depend substantially on the foods used to replace carbohydrate. Nutritional quality therefore remains important, including the sources of dietary fat and protein, fiber intake, micronutrient adequacy, and the overall dietary pattern.

The ADA Standards of Care recognize reducing overall carbohydrate intake as one strategy that may improve glycemia for some adults with diabetes.[7] Current recommendations emphasize individualized medical nutrition therapy rather than prescribing a single ideal percentage of calories from carbohydrate, protein, or fat. When carbohydrate intake is reduced, dietary quality should remain a priority, with an emphasis on limiting refined carbohydrates, added sugars, and highly processed foods while incorporating nutrient-dense, minimally processed foods.

Effects on Glycemia and Weight

Clinical trials and meta-analyses generally demonstrate improvements in HbA1c with carbohydrate-restricted dietary interventions, although the magnitude of benefit varies according to baseline glycemia, degree of carbohydrate restriction, medication use, adherence, and duration of follow-up. Some meta-analyses have reported modest additional reductions in HbA1c compared with control diets, often in the range of approximately 0.3 percent, together with improvements in fasting glucose and body weight.[8] Differences between dietary approaches are often more apparent during the first three to six months and may diminish with longer follow-up.

Changes in HbA1c should also be interpreted in the context of concurrent medication adjustments. Improved glycemia may permit reductions in glucose-lowering medications, particularly insulin and insulin secretagogues, when clinically appropriate. As a result, HbA1c alone may not fully capture treatment benefit in studies in which medication burden decreases while glycemic control is maintained.

Weight loss frequently accompanies carbohydrate-restricted dietary interventions, particularly when they also reduce total energy intake. Improvements in glycemia may therefore reflect a combination of reduced dietary carbohydrate exposure, changes in energy intake, and the metabolic benefits associated with intentional weight loss. These overlapping effects should be considered when evaluating an individual patient’s response.

Long-Term Adherence and Sustainability

Long-term sustainability remains an important consideration. Many trials demonstrate favorable glycemic and weight outcomes during the first several months, while differences between low-carbohydrate and comparison diets often narrow by 12 months or with longer follow-up. Changes in dietary adherence over time, as well as improvements within comparator groups, may contribute to this pattern.

These findings reinforce the importance of selecting a dietary approach that a patient can safely, realistically, and preferably maintain over time. Follow-up should include assessment of dietary quality and nutritional adequacy, glycemic response, medication requirements, weight trajectory, cardiometabolic risk factors, and the patient’s preferences and ability to sustain the dietary pattern.

Carbohydrate restriction should not be viewed as the only evidence-supported dietary strategy for T2D. Mediterranean, DASH, and appropriately designed plant-forward or plant-based dietary patterns can also support glycemic and cardiometabolic health. Nutrition therapy should ultimately be individualized according to metabolic goals, comorbidities, cultural and food preferences, medication regimen, nutritional needs, and long-term sustainability.

Medication Adjustment Considerations During Low-Carbohydrate Diets

Substantial carbohydrate restriction can reduce postprandial glucose concentrations rapidly, sometimes beginning with the first meals after dietary changes are implemented. For patients taking glucose-lowering medications, particularly insulin or insulin secretagogues, medication review should occur before or at the time carbohydrate intake is substantially reduced. More frequent glucose monitoring, including use of continuous glucose monitoring (CGM) when appropriate, may be helpful during this transition.

Insulin and Sulfonylureas

Insulin and sulfonylureas require particular attention because reducing carbohydrate intake without appropriate medication adjustment can increase the risk of hypoglycemia. Patients using these therapies should have an individualized plan for glucose monitoring and medication adjustment when making substantial changes in carbohydrate intake.

Reductions in prandial insulin may be necessary when meal carbohydrate content decreases substantially. Basal insulin adjustments should be individualized according to glucose patterns, diabetes type and duration, endogenous insulin reserve, degree of carbohydrate restriction, and other glucose-lowering therapies. In patients who require insulin to prevent ketosis, particularly those with type 1 diabetes, basal insulin should not be discontinued solely because carbohydrate intake has been reduced.

Sulfonylurea doses may similarly need to be reduced or discontinued when clinically appropriate as glucose concentrations improve. Published guidance provides practical frameworks for medication adjustment when initiating a carbohydrate-restricted dietary intervention.[9]

SGLT2 Inhibitors

Sodium-glucose cotransporter 2 (SGLT2) inhibitors require particular caution in patients considering a very low-carbohydrate or ketogenic dietary pattern. Although diabetic ketoacidosis (DKA) is uncommon among adults with T2D treated with SGLT2 inhibitors, these medications increase the risk of DKA, which may occur with glucose concentrations that are lower than typically expected in DKA, often referred to as euglycemic DKA.

Very low carbohydrate intake, prolonged fasting or markedly reduced caloric intake, acute illness, dehydration, surgery, and insufficient insulin are among the factors that can increase this risk. Case reports have described euglycemic DKA in individuals combining SGLT2 inhibitor therapy with ketogenic diets.[10]

Because of this risk, ketogenic or very low-carbohydrate dietary patterns warrant particular caution in patients taking an SGLT2 inhibitor and generally should not be initiated without review of the medication regimen and dietary plan by the treating clinician. Patients taking SGLT2 inhibitors should also receive education about symptoms of ketoacidosis, situations in which the medication may need to be temporarily withheld, and appropriate sick-day management. Importantly, a normal or only moderately elevated glucose concentration does not exclude DKA in a symptomatic patient taking an SGLT2 inhibitor.

Metformin

Metformin can generally be continued during carbohydrate restriction because it carries a low intrinsic risk of hypoglycemia when used alone.[11] Routine dose reduction is generally unnecessary solely because carbohydrate intake has decreased. Continued use and dosing should be reassessed over time according to glycemic response, tolerability, kidney function, and the patient’s overall treatment goals.

GLP-1–Based Therapies

GLP-1 receptor agonists and related incretin-based therapies, including dual GIP/GLP-1 receptor agonist therapy, can generally be used with a carbohydrate-restricted dietary approach without substantially increasing hypoglycemia risk when used without insulin or insulin secretagogues.[12] These therapies may provide complementary benefits for glycemic management and weight reduction.

Clinicians should nevertheless assess dietary intake, gastrointestinal tolerability, hydration, and the rate and magnitude of weight loss, particularly when appetite suppression is substantial. Attention to adequate protein, fiber, micronutrient, and overall energy intake may be especially important when pharmacologic appetite suppression is combined with substantial dietary restriction. When incretin-based therapy is used with insulin or a sulfonylurea, doses of those medications may need to be adjusted to reduce hypoglycemia risk.

Combination Therapy

SGLT2 inhibitors and GLP-1–based therapies are increasingly used together because their clinical effects may be complementary in appropriately selected patients, including benefits related to glycemic management, cardiovascular and kidney risk reduction, and weight management.[13] The magnitude and type of benefit depend on the individual medication and the patient’s underlying cardiovascular, kidney, and metabolic risk.

When combination pharmacotherapy is used, medication-specific precautions remain important. In particular, concurrent GLP-1–based therapy does not eliminate the risk of SGLT2 inhibitor–associated euglycemic DKA during severe carbohydrate or caloric restriction.

Medication management should therefore be individualized according to diabetes type, degree of carbohydrate restriction, glucose patterns, medication regimen, risk of hypoglycemia or ketosis, comorbidities, nutritional intake, and the patient’s overall treatment goals. Close follow-up may be particularly important during the initial transition to substantial carbohydrate restriction.

Patient Selection and Individualization

A low-carbohydrate eating pattern may be appropriate for some adults with type 2 diabetes (T2D), but the decision should be individualized rather than based on a specific clinical profile. Factors to consider include glycemic goals, current eating patterns, food preferences, weight-management goals, comorbidities, medication use, nutritional needs, cultural considerations, socioeconomic factors, and the patient’s ability and willingness to sustain the eating pattern over time.

Some patients may find carbohydrate restriction particularly useful for reducing postprandial glucose excursions, improving overall glycemia, or supporting intentional weight loss. Others may prefer a Mediterranean, DASH, plant-forward, or other evidence-based dietary pattern. The goal is not to identify a single optimal diet for T2D, but to select a nutritionally adequate eating pattern that aligns with the patient’s clinical needs, preferences, and treatment goals.

Certain patients require additional clinical consideration and monitoring. Individuals using insulin or sulfonylureas may require medication adjustment and closer glucose monitoring because carbohydrate reduction can increase the risk of hypoglycemia if glucose-lowering therapy is not modified appropriately. Patients taking SGLT2 inhibitors require particular caution because very-low-carbohydrate or ketogenic eating patterns may increase the risk of diabetic ketoacidosis.

For patients with chronic kidney disease, dietary recommendations should be individualized according to kidney function, nutritional status, and recommended protein intake. Carbohydrate restriction does not inherently require a high-protein diet, and protein intake should remain appropriate for the individual patient. A history of an eating disorder or problematic restrictive eating also warrants careful assessment before recommending a highly restrictive dietary pattern.

Type 1 diabetes requires separate consideration. Evidence regarding very-low-carbohydrate and ketogenic eating patterns in type 1 diabetes remains more limited, and concerns related to insulin adjustment, hypoglycemia, ketosis, and diabetic ketoacidosis require careful clinical supervision. Recommendations developed for adults with T2D should therefore not be automatically extrapolated to individuals with type 1 diabetes.

Ultimately, the most appropriate eating pattern is one that is safe, nutritionally adequate, culturally and financially feasible, and sustainable for the individual patient. When available, referral to a registered dietitian nutritionist experienced in diabetes care can help translate carbohydrate-reduction goals into a balanced and practical long-term eating plan.

Supporting Patients With Carbohydrate Restriction

Successful implementation of a carbohydrate-restricted eating pattern requires individualized planning, attention to dietary quality, appropriate medication management, and ongoing follow-up. Before a patient substantially reduces carbohydrate intake, clinicians should review the medication regimen, with particular attention to insulin and insulin secretagogues because of the risk of hypoglycemia and to sodium-glucose cotransporter 2 (SGLT2) inhibitors because of the risk of diabetic ketoacidosis (DKA).

The degree of carbohydrate restriction should be individualized through shared decision-making rather than based on a single carbohydrate target. Relevant considerations include glycemic and weight-management goals, current eating patterns, food preferences, cultural and socioeconomic factors, nutritional needs, comorbidities, medication use, and the patient’s ability and willingness to follow the dietary approach.

Patients taking glucose-lowering medications may require more frequent glucose monitoring when initiating or intensifying carbohydrate restriction, particularly when insulin or insulin secretagogues are used. Continuous glucose monitoring (CGM), when available and appropriate, can provide additional information about glucose patterns during dietary and medication changes. The timing and intensity of follow-up should reflect the magnitude of these changes and the patient’s clinical circumstances. Assessment may include glucose patterns, hypoglycemia, HbA1c, weight trajectory, medication requirements, lipid profile, kidney function when clinically indicated, dietary quality and nutritional adequacy, and overall tolerability.

Very low-carbohydrate or ketogenic eating patterns require additional consideration. The 2026 ADA Standards of Care identify very low-carbohydrate eating patterns as a potential risk factor for DKA in people receiving SGLT inhibition and recommend discouraging ketogenic eating patterns in individuals at risk for DKA who are treated with these medications. Patients taking SGLT2 inhibitors should receive education about DKA symptoms, circumstances that may increase risk, appropriate sick-day management, and ketone monitoring when clinically indicated.

Referral to a registered dietitian nutritionist (RDN), preferably one experienced in diabetes and obesity management, can help translate individualized carbohydrate goals into a nutritionally adequate and practical eating pattern. Counseling should emphasize overall dietary quality rather than carbohydrate restriction alone. This includes adequate protein, fiber, micronutrients, and appropriate sources of dietary fat while prioritizing nutrient-dense, minimally processed foods and limiting refined carbohydrates, added sugars, and highly processed foods.

Ongoing follow-up is important because dietary adherence, preferences, medication requirements, weight, and metabolic responses may change over time. Clinicians should periodically reassess whether the dietary approach continues to support the patient’s glycemic and metabolic goals, remains nutritionally adequate and acceptable, and can be followed safely. The degree of carbohydrate restriction can be modified over time according to the patient’s response and preferences.

Carbohydrate restriction is one of several evidence-based nutrition strategies that may be considered for adults with T2D. Mediterranean, DASH, plant-forward, and other evidence-based dietary patterns may also support glycemic and cardiometabolic health. The choice of dietary approach should be individualized according to metabolic goals, nutritional needs, comorbidities, medications, cultural and food preferences, access to foods and resources, and long-term feasibility.

For broader guidance on nutrition therapy in obesity and metabolic disease, the Obesity Algorithm® provides evidence-based recommendations to help clinicians individualize dietary interventions within comprehensive obesity care.