Hooper et al included this trial by Black 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
General guidelines for a low-fat diet effective in the management and
prevention of nonmelanoma skin cancer (1997) [3]
Purpose
Ecological studies at the time and animal studies found a relationship
between fat intake and the incidence of skin cancers and actinic keratosis (potentially precancerous
tissue) [1] [2]
Methods
133 people with a previous diagnosis of skin cancer (define) were
randomised to a low fat group or a control group.
The low fat group
attended 8 weekly classes where they were advised to reduce fat intake to 20%,
keep protein at 15% and increase carbohydrate to 65% and to avoid calorie
deficit. Foods containing sufficient vitamins and
minerals to meet the recommended dietary allowances for adults were emphasized.
The patients were taught behavioral techniques such as stimulus control,
self-monitoring, and cognitive behavioral self-management to help them comply
with the dietary regimen” [1] [2] [3]. “The
primary strategy recommended for increasing carbohydrate intake was to increase
consumption of grains, fruits, and vegetables. This strategy introduces an
additional potential variable; i.e., a statistically significant inverse
relationship has been reported between nonmelanoma skin cancer and high
vegetable intake”. [3]
Results
Fat intake was maintained well at a little over 20% and despite advice to increase complex carbohydrates to
maintain weight (which they did: 264.5g vs. 303.5g), the low fat group had a significant
decrease in calorie intake and significant weight loss [1] [2] [3]
Consistent with the advice to consume more fruits, vegetables and grains,
the low fat group increased their fibre and vitamin C intake, but not by much [3]
The low fat group had a
significantly lower incidence of actinic keratoses [1] and
total skin cancers [2] [3]
Hooper et al included
this trial as a reduced fat trial in their 2012 meta-analysis and as a reduced
SFA trial in their 2015 meta-analysis.
Similar to the other low fat trials, while it’s very appropriate to
include this as a reduced fat trial, it is less appropriate to include this as
a reduced SFA trial due to the simultaneous decreases in MUFA and PUFA as
well. Hooper et al
reports the following results in their meta-analyses. The incidence of CVD events and CVD mortality
was not published, but it was reported that 1 person died in the low fat group
and 2 people died in the control group.
They also flagged the trial as having high risk of ‘free of
systematic difference in care’ and low risk of ‘free of dietary differences
other than fat’
Low Fat Group (N
= 66)
|
Control Group (N
= 67)
|
|
CVD Events
|
0
|
2
|
CVD Mortality
|
0
|
2
|
Total Mortality
|
1
|
2
|
The paleo explanation for the reduced incidence of skin cancer would be the lower PUFA intake in the intervention.
ReplyDeleteThe authors get it wrong here -
"Nor was the type of fat consumed a contributing factor, since the ratio of polyunsaturated fat to saturated fat averaged 0.66 in the control group and 0.67 in the dietary-intervention group over the two-year period."
If the ratio was the same but the fat intake was reduced - from 40% to 20% - then PUFA intake was halved. PUFA is mostly linoleate and US linoleate intake by 1990s was around 7-8% - so this may have been a good test of reducing PUFA to optimal 4%.
The PUFA explanation is possible, and probably more likely than their suggestion of calorie restriction or of differences whole plant foods, vitamin C, etc.
DeleteI did a PubMed search and it doesn't seem to be well researched. At face value, some studies support it and others don't. Interesting that the lead author just published a paper saying omega 6 PUFAs promote UV-induced skin cancer
It's also noteworthy that the dietary effect was delayed, perhaps related to a change in fatty acid composition to more SFA/MUFA?
The role of nutritional lipids and antioxidants in UV-induced skin cancer.
http://www.ncbi.nlm.nih.gov/pubmed/25961684
This comment has been removed by the author.
ReplyDelete