Sunday, August 2, 2015

Ley et al (Low Fat Diet for Glucose Intolerance)

Hooper et al included this trial by Ley et al as a reduced fat trial in their 2012 meta-analysis and as a reduced SFA trial in their 2015 meta-analysis

Studies Associated with the Trial

Effects of reduced-fat diets consumed ad libitum on intake of nutrients particularly antioxidant vitamins (1999) [1]
Long-term (5-year) effects of a reduced-fat diet intervention in individuals with glucose intolerance (2001) [2]
Long-term effects of a reduced fat diet intervention on cardiovascular disease risk factors in individuals with glucose intolerance (2004) [3]


176 people aged > 40 with glucose intolerance (2h glucose = 7.0 - 11.0 mmol/l) were randomised to reduced fat group or a control group for 1 year.  86% had a BMI > 25.  The groups were similar at baseline [1] [2] [3]

The reduced fat diet was ad libitum.  “Participants in the reduced-fat group began a 1-year structured program aimed solely at reducing the total amount of fat in their usual diet. The program involved education on reducing dietary fat intake, personal goal setting, self-monitoring, and evaluation through a series of monthly small-group sessions, which were held in a variety of suburban localities to promote higher participation rates” [1] [2] [3]

“Participants in the control group received nutrition advice at the time of entering the trial. Most control group participants received only general advice about healthful eating that was consistent with the New Zealand Food and Nutrition Guidelines. Those with nutrition-related problems such as elevated serum cholesterol levels or obesity also received standard dietary information about these problems” [1]

* Of the 176 started, 26 dropped out (16 control, 10 reduced fat), 13 were withdrawn from the study because of major illness, death, pregnancy, or moving out of the region (4 control, 9 reduced fat) and 27 had incomplete dietary records, leaving 110 people who completed the study with full dietary data [1] [2] [3]

** At the end of the first year there were significantly fewer smokers in the reduced fat group (9% vs. 23%) [1], but there were significantly more smokers in the reduced fat group among those who completed the trial (23% vs. 6%) [3].  At the end of the first year 20% of the reduced fat group reported an increase in exercise vs. 9% of the control group (P = 0.002).  “At the end of year 2, 21% of the RF group reported that they were exercising as a means to lose weight compared with 12% of the control group (P = 0.087), but by the end of year 3, these percentages had reversed (13 vs. 21%, P = 0.13)”. [2]


The reduced fat group lowered their intake of fat and didn’t increase carbohydrate and fibre consumption, so total calories decreased (see table below)

There isn’t much to report regarding micronutrient intakes as it wasn’t really affected by the reduced fat diet and there weren’t any significant differences, except that it was consistently kind of low.  As such, serum retinol and a-tocopherol were similar at the end of the study, although serum beta carotene was higher in the reduced fat group (0.66 vs. 0.45 umol/l, p < 0.009) despite similar intakes, which may be related to a slight decrease in alcohol intake in the reduced fat group and a slight increase in the control group [1]

Reduced Fat Group
Control Group
Energy (kcal)
14.6 (4.4%)
10.0 (3.5%)
17.5 (4.5%)
22.1 (5.8%)
34.6 (13.8%)
19.9 (9.9%)
38.3 (14.2%)
36.2 (13.5%)
29.5 (11.8%)
17.6 (8.8%)
34.1 (12.7%)
31.9 (11.8%)
13.2 (5.5%)
8.1 (4.0%)
13.3 (5.1%)
12.3 (4.8%)
Fibre (g)

The main results are presented below.  Left graphs from [2], right graphs from [3].  In these graphs the most compliant in reduced fat group = solid line; least compliant in reduced fat group = dotted line; control group = dashed line.  Remember that the intervention only lasted for 1 year.  Things that might be noteworthy include:

·         The significant weight loss among the most compliant to the reduced fat diet, which unfortunately was not maintained
·         The reduced fat diet didn’t lower HDL-C or raise triglycerides initially (which may be related to weight loss), therefore the total-C:HDL-C ratio went down rather than up
·         The most compliant to the reduced fat diet had some improvements in fasting glucose and 2h glucose.  Low carbohydrate diets are not the only option for people with insulin resistance, impaired glucose tolerance or type 2 diabetes

Neither of the studies reported CHD/CVD events or deaths and so the following figures come from the meta-analyses by Hooper et al.  The reduced fat group consistently had slightly fewer events and deaths, but due to the low numbers none of these were close to significance

Reduced Fat Group
(N = 88)
Control Group
(N = 88)
Myocardial Infarction
CHD Events
CVD Events
CVD Mortality
Total Mortality

Hooper et al included this trial in their 2012 meta-analysis as a reduced fat trial and in their 2015 meta-analysis as a reduced SFA trial (SFA reduced by at least 20%).  It’s a lot more appropriate to classify this as a reduced fat trial rather than a reduced SFA trial due to the simultaneous decreases in MUFA and PUFA as well.  Hooper et al also flagged the trial as having a ‘high risk’ of being ‘free of systematic difference in care’.  In addition, Hooper et al’s 2015 meta-analysis only includes trials that lasted for at least 24 months.  While this trial had a 5 year long follow up period, it only had a 1 year intervention period so it arguably doesn’t meet the 24 month criteria.

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