Sunday, July 26, 2015

Black et al (Low Fat Diet for Skin Cancer)

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

Effect of a Low-Fat Diet on the Incidence of Actinic Keratosis (1994) [1]
Evidence that a low-fat diet reduces the occurrence of non-melanoma skin cancer (1995) [2]
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]

“The diet of the patients assigned to the control group was not changed” [1]

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

3 comments:

  1. The paleo explanation for the reduced incidence of skin cancer would be the lower PUFA intake in the intervention.
    The 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%.

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    1. The PUFA explanation is possible, and probably more likely than their suggestion of calorie restriction or of differences whole plant foods, vitamin C, etc.

      I 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

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