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.