Effects of Whole Fruit on Blood Sugar in People With Type 2 Diabetes

Diabetes is one of the top three drivers of healthcare costs in the U.S., and nearly half of Americans will develop either diabetes or prediabetes in their lifetime. It is therefore critical to find new strategies to treat or reverse diabetes.

One such approach is adopting a healthy diet, which can dramatically improve blood sugar levels in adults with type 2 diabetes and even induce diabetes remission in some patients. Despite this, not much is known about which food groups are most effective at improving blood sugar levels in patients with diabetes.

Although individuals with type 2 diabetes are often advised to reduce carbohydrate intake, current dietary guidelines also recommend consuming fruit and other carbohydrate-rich foods. This has led to confusion among patients and clinicians about whether eating fruit, particularly in larger amounts, is beneficial or harmful for blood sugar and overall health. Whole fruit differs from many other carbohydrate sources in that whole fruit is rich in fiber, vitamins, minerals, and bioactive plant compounds, while being relatively low in energy density.

Most prior research examining the effects of whole fruit in people with type 2 diabetes has been epidemiologic, focused on individual fruits, or combined whole fruit with fruit juice and/or vegetables into a single food category. As a result, it is unknown how whole fruit, as a food category, affects glycemic control and cardiovascular health.

The investigators previously found that a whole-fruit-rich, Mediterranean-style diet improved blood sugar control and blood pressure in patients with type 2 diabetes and even allowed some patients to wean off all anti-hyperglycemic medications. The investigators will conduct a follow-up study to determine the effects of whole fruit alone on glycemic control, liver fat, and cardiovascular risk factors. The study will be a single-arm controlled feeding study to determine the effects of eating a large amount of whole fruit for 17 weeks on glycemic control (Aim 1), liver fat (Aim 2a), and cardiovascular disease risk factors (Aim 2b) in patients with insulin-independent type 2 diabetes. The primary measures of glycemic control will be mean 24-hour glucose levels (as measured by continuous glucose monitoring) and mean 3-hour glucose levels (as measured during a 3-hour oral glucose tolerance test). These assessments will be supplemented by, and interpreted in light of, other glycemic outcomes, which are listed as outcomes #3-9 below.

By providing controlled, high-quality evidence, this study will determine whether whole fruit is good or bad for patients with type 2 diabetes and will improve dietary guidelines for the hundreds of millions of individuals with type 2 diabetes.

Inclusion criteria

• Aged ≥18 years
• Diagnosed with type 2 diabetes
• HbA1c between 6.5-12.0%
• Fasting C-peptide level ≥0.5 ng/ml, indicating the patient does not have beta-cell failure, as measured at screening

Exclusion criteria

• On insulin
• Evidence of latent autoimmune diabetes (LADA) or maturity-onset diabetes of the young (MODY)
• Estimated glomerular filtration rate (eGFR) <45 ml/min per 1.73 m²
• Heart attack in the past 6 months or severe/unstable heart failure
• On weight loss medication, including GLP-1 receptor agonists (e.g., semaglutide, dulaglutide)
• Change in the dosage of a chronic medication that may affect study endpoints within the past 3 months
• Clinically significant laboratory abnormality (e.g., abnormal hemoglobin levels)
• Significant gastrointestinal disease, major gastrointestinal surgery, or gallstones
• Significant cardiovascular, renal, cardiac, liver, lung, adrenal, or nervous system disease that might compromise participant safety or data validity
• Evidence of cancer (other than non-melanoma skin cancer) within the last 5 years
• Lost or gained more than 5 lbs (or more than 2% of body weight if the patient weighs >250 lbs) of weight in the past 2 months
• Pregnant, planning to become pregnant in the next 6 months, or breastfeeding
• Major psychiatric condition that would affect the ability to participate in the study
• Not able to eat the provided study meals (e.g., food allergies)
• Behavioral factors or circumstances that may impede adherence to the dietary intervention
• Not able to undergo the MRI scan (e.g., due to claustrophobia, implanted metal objects, or body girth ≥60 cm)