High-protein (HP) diets are popular and evidence indicates they are more likely to be adhered to and produce more sustained weight loss, particularly under ad libitum conditions. They also improve glucose control and so may be helpful for treatment of Type 2 Diabetes (T2D), particularly in the short-term, possibly via an improvement in insulin secretion. Indeed, HP diets may be uniquely effective at promoting insulin secretion in T2D, but further research is needed to understand why HP. Thus, there is an urgent need to determine how HP diets affect T2D pathophysiology of insulin secretion and action using direct measures of β-cell dysfunction and insulin sensitivity. It is also imperative to know how the type of protein (animal vs. non-animal) affects insulin secretion in order to ultimately obtain an environmentally and economically sustainable HP diet that can improve glucose control and T2D pathophysiology in the long-term as well as providing patients with a greater choice for dietary management of T2D.

Inclusion Criteria:

• Aged 40-70 y
• Body-mass index of 27-45 kg/m2
• Diagnosed with T2D with their most recent HbA1c value greater than 6.0% (>43 mmol/mol) and receiving dietary advice and/or antidiabetic medication (metformin, DPP-4 inhibitors only).
• Males and females

Exclusion Criteria:

• Habitual dietary intake of <0.6 or >1.2 g/kg/day protein (determined from dietary history interview given at screening)
• Current use of insulin
• HbA1c of 12% or more (≥108 mmol/mol)
• Weight loss of more than 5 kg within the past 6 months
• A recent estimated glomerular filtration rate (eGFR) of less than 30 mL/min,
• Heart failure,
• Participation in another clinical research trial, substance abuse, known cancer, myocardial infarction within the previous 6 months, current treatment with anti-obesity drugs, pregnancy or consideration of pregnancy, and hospital admission for depression or use of antipsychotic drugs.