The aim of the present systematic review and meta-analysis was to examine the long-term effects (≥ 12 months) of high-fat (HF) v. low-fat (LF) diet consumption on the indicators of glycaemic control as well as cardiovascular risk factors in pre-diabetic and diabetic individuals. Literature search was carried out using the electronic databases MEDLINE, Embase and the Cochrane Trial Register until November 2013. Study-specific weighted mean differences (MD) were pooled using a random-effects model of the Cochrane software package Review Manager 5.1 and Stata 12.0 was used for meta-regressions. A total of fourteen trials met the inclusion criteria and a maximum of 1753 subjects were included in the meta-analysis. HF regimens were found to result in a significant decrease in TAG levels (MD -0·19 mmol/l, 95 % CI -0·23, -0·14, P< 0·001; I² = 0 %, P= 0·58) and diastolic blood pressure (MD -1·30 mmHg, 95 % CI -1·73, -0·87, P< 0·001; I² = 0 %, P= 0·60) and a significant increase in HDL-cholesterol levels (MD 0·05 mmol/l, 95 % CI 0·01, 0·08, P= 0·01; I² = 57 %, P= 0·01). In addition, MD in the reductions of fasting glucose levels (-0·41 mmol/l, 95 % CI -0·74, -0·08, P= 0·01; I² = 56 %, P= 0·02) were significantly high in patients with type 2 diabetes adhering to a HF diet. HF and LF diets might not be of equal value in the management of either pre-diabetes or type 2 diabetes, leading to emphasis being placed on the recommendations of HF diets.