Dietary strategies for alleviating health complications associated with type 2 diabetes (T2D) are being pursued as alternatives to pharmaceutical interventions. Berries such as blackcurrants that are rich in polyphenols may influence carbohydrate digestion and absorption and thus postprandial glycaemia. In addition berries have been reported to alter incretins as well as to have anti-oxidant and anti-inflammatory properties that may also affect postprandial glycaemia. This study investigated the acute affect blackcurrants on glucose metabolism in overweight/obese volunteers .

Sixteen overweight/obese volunteers from the Aberdeen area will be recruited into a randomised controlled study. Volunteers will be randomised into four groups matched for BMI and age and given 200 grams of blackcurrants (which contain anthocyanins) or greencurrants (which naturally contain no anthocyanins), followed by an OGTT.

The consumption of the currants will be followed by an oral glucose tolerance test (OGTT) with Polycal (complex carbohydrate) or glucose (simple carbohydrate) as the carbohydrate load.

There will be a one week minimum wash out period between each intervention. All interventions will be randomised and blinded as far as possible in a cross-over design where the volunteers are acting as their own control. The volunteers will be asked to consume a low phytochemical diet three days prior to taking the currants all occasions. In addition, they will be asked to record what they ate over the same period in a simple food diary.

The following intervention will be carried out on 16 overweight/obese male/postmenopausal female non-smoker volunteers:

1. Control: sugar matched (matched to currant sugar content) water with polycal (complex carbohydrate load)
2. Blackcurrants (which contain anthocyanins; 200grams) with polycal (complex carbohydrate load)
3. Blackcurrants (which contain anthocyanins; 200grams) with glucose (simple carbohydrate load)
4. Greencurrants (which naturally contain no anthocyanins; 200grams) with polycal (complex carbohydrate load)

Note: the polycal will contain the equivalent glucose load as given in intervention 3 assuming complete hydrolysis of all carbohydrates.

Inclusion Criteria:

• Obese male or female (postmenopausal) healthy non-smoking volunteers (BMI over 25kg/m2)
• Aged >21 and <70 years

Exclusion Criteria:

• Medical exclusion criteria

• Chronic illness, including:

  • thromboembolic or coagulation disease
  • unregulated thyroid disease
  • kidney disease
  • hepatic disease
  • severe gastrointestinal disorders
  • pulmonary disease (e.g. chronic bronchitis, COPD)
  • diabetes

• Alcohol or any other substance abuse

• Eating disorders

• Psychiatric disorders (including severe depression, lithium treatment, schizophrenia, severe behavioural disorders)

• Non-postmenopausal women

• Medication exclusion criteria

• Oral steroids

• Tricyclic antidepressants, neuroleptics

• Anticoagulants

• Digoxin and anti-arrhythmics

• Chronic use of anti-inflammatories (e.g. high doses of aspirin, ibuprofen), Insulin, -Sulphonylureas, Thiazolidinediones (glitazones), metformin.

• Anti-obesity medication e.g. Orlistat