Tuesday, February 28, 2012

Vegans don't live longer than vegetarians or meat eaters

Background: If we take a look at wikipedia (1), we see that both vegetarians and vegans have lower mortality rates from heart disease, compared to regular meat eaters:

A 1999 meta-analysis of five studies comparing vegetarian and non-vegetarian mortality rates in Western countries found that the mortality rate due to ischemic heart disease was 26 percent lower among vegans compared to regular meat eaters, but 34 percent lower among lacto-ovo vegetarians (vegetarians that eat dairy products and eggs) and pescetarians (those that eat fish but no other meat).

Wikipedia also states that:

No significant difference in mortality was found from other causes.
This line suggests that both vegetarians and vegans may live longer than regular meat eaters. Results from the article referred to (2) can be seen in the following table:

In the table we see that occasional meat eaters, vegetarians and fish eaters had similar risks of mortality from all-causes. These were lower than mortality rates from regular meat eaters. However, vegans had mortality rates identical to those from regular meat eaters.

Conclusion: a meta-analysis of 5 prospective studies showed that both vegetarians and vegans had lower mortality rates from heart disease than regular meat eaters. However, in the case of vegans, this did not lead to lower risk of mortality from all causes.

1) Wikipedia. Veganism. Wikipedia page last modified on 26 February 2012. http://en.wikipedia.org/wiki/Veganism
2) Key TJ et al. Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am J Clin Nutr. 1999 Sep;70(3 Suppl):516S-524S. http://www.ajcn.org/content/70/3/516S.full

Sunday, February 26, 2012

Whole grains may decrease diabetes risk

Background: High calcium intake has been linked to lower risk of diabetes in the past (1), though this association may have been confounded by magnesium intake (2). Likewise, high magnesium intake has also been linked to lower risk of diabetes (3).
Whole grains contain phytic acid which has been linked to decreased absorption of magnesium, calcium and other minerals from the gastrointestinal tract (4). The combination of these factors is sometimes used to prove that whole grains are to increase diabetes risk. However, the theory is very simplistic not taking into account other nutrients in whole grains and not taking into account the complexity of the human body.
If whole grains are to increase diabetes risk, then it would be expected that people with high intakes of whole grains have higher risk of diabetes than people with lower intakes. This association can be examined in human trials.

Methods: A group of scientists searched the scientific databases MEDLINE and EMBASE for prospective cohort studies examining whole grain intake in relation to risk of type 2 diabetes (5). Results from 6 cohorts could be included in the following meta-analysis. The studies included a total of 286,125 participants and 10,944 cases of diabetes type 2.

Table 1:

Results: Table 1 shows results from the 6 individual studies as well as the average (combined) effect. A 21% lower risk of diabetes was found for each 2 serving per day increment in intake of whole grains (RR = 0.79; 95% CI = 0.72-0.87). Table 1 also shows that a protective effect was found in all 6 cohorts. And that protective effects were significant in all cohorts, except for the cohort examined by Montonen et al.

Conclusion: Results from prospective cohort studies consistently show that subjects with higher whole grain consumption have lower risk of diabetes type 2.

1) Pittas AG et al. The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis.J Clin Endocrinol Metab. 2007 Jun;92(6):2017-29.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2085234/?tool=pubmed
2) Dong JY et al. Dietary calcium intake and risk of type 2 diabetes: possible confounding by magnesium. Eur J Clin Nutr. 2012 Feb 8. doi: 10.1038/ejcn.2012.5. http://www.ncbi.nlm.nih.gov/pubmed/22318650
3) Dong JY et al. Magnesium intake and risk of type 2 diabetes: meta-analysis of prospective cohort studies. Diabetes Care. 2011 Sep;34(9):2116-22. http://www.ncbi.nlm.nih.gov/pubmed/21868780
4) Zhou JR et al. Phytic acid in health and disease. Crit Rev Food Sci Nutr. 1995 Nov;35(6):495-508. http://www.ncbi.nlm.nih.gov/pubmed/8777015
5) de Munter JS et al. Whole grain, bran, and germ intake and risk of type 2 diabetes: a prospective cohort study and systematic review. PLoS Med. 2007 Aug;4(8):e261. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1952203/?tool=pubmed

Saturday, February 25, 2012

Berries do not decrease cancer risk

Background: berries are said to decrease cancer risk. If we google for "berries cancer" we see that pretty much all titles suggest this to be true. These ideas are based on the assumption that berries include several nutrients thought to be healthy, such as vitamins, minerals and polyphenols. But if we take a closer look at the evidence, we see that articles are consistently based on either:
-Animal research.
-Studies in cell lines.
-Nothing. No references are given to back up the claim.

If berries are to decrease cancer risk in humans, it would be logical that humans with higher intake of berries have lower cancer risk than humans with lower intake of berries.

Methods: I searched the Pubmed database for prospective (= cohort) studies relating berry consumption to cancer risk for 7 major types of cancer. Details of the search term and inclusion criteria can be found on my other internetsite (1).

A) Breast cancer:
Type of berries:
2) Adebamowo CA (2005)
90,630 women
RR = 1.25 (0.86-1.80; P = 0.84)
One study was found. Blueberries did not protect against breast cancer risk.

B) Colorectal cancer:
Type of berries:
3) Michels KB (2000)
88,764 women
No significant association with colon or rectal cancer
3) Michels KB (2000)
47,325 men
No significant association with colon or rectal cancer
4) Lin J (2005)
36,976 women
No significant association with colorectal cancer
Two studies were found, including three cohorts. Blueberries did not protect against colorectal cancer risk. No relative risks were provided in the articles referred to.

C) Lung cancer:
Type of berries:
5) Knekt P (1997)
9,959 men and women
Total berries (lingonberries, blueberries, black currants, raspberries and gooseberries)
RR = 1.80 (1.11-2.93)
6) Cutler GJ (2008)
34,708 women
Total berries (mostly blueberries and strawberries)
No association was found
7) Feskanich D (2000)
77,283 women
No association was found
7) Feskanich D (2000)
47,778 men
No association was found
8) Hirvonen T (2001)
27,110 men
Total berries
A nonsignificant protective effect.
Four studies were found, including five cohorts. Only one study (Knekt P. 1997) provided a relative risk which showed a significant 80% increased risk of lung cancer. No other significant associations were found.

D) Pancreatic cancer risk:
Type of berries:
9) Bobe G (2008)
27,111 men
Total berries
HR = 0.88 (0.63-1.24; P = 0.94)
10) Vrieling A (2009)
478,400 men and women
Total berries (e.g., strawberries and raspberries
HR = 0.90 (0.66-1.23; P = 0.61)
Two studies were found. No associations were found.

E) No prospective studies were found examining berry consumption in relation to esophageal, ovarian, or prostate cancer risk.

Conclusion: prospective cohort studies consistently show that subjects with higher intakes of berries do not have lower cancer risk.

Limitations: results presented here were limited to only 7 types of cancer. However, these include major types of cancer: breast, colorectal, esophageal, lung, ovarian, pancreatic and prostate cancer risk. And no protective effects were found in 2 studies examining total cancer risk (1).

1) Hoenselaar R. Cancer and diet. A systematic review. http://canceranddiet.nl/
2) Adebamowo CA et al. Dietary flavonols and flavonol-rich foods intake and the risk of breast cancer. Int J Cancer. 2005 Apr 20;114(4):628-33. Int J Cancer. 2005 Apr 20;114(4):628-33. http://www.ncbi.nlm.nih.gov/pubmed/15609322
3) Michels KB et al. Prospective study of fruit and vegetable consumption and incidence of colon and rectal cancers. J Natl Cancer Inst. 2000 Nov 1;92(21):1740-52.  http://jnci.oxfordjournals.org/content/92/21/1740.full
4) Lin J et al. Dietary intakes of fruit, vegetables, and fiber, and risk of colorectal cancer in a prospective cohort of women (United States). Cancer Causes Control. 2005 Apr;16(3):225-33. http://www.ncbi.nlm.nih.gov/pubmed/15947874
5) Knekt P et al. Dietary flavonoids and the risk of lung cancer and other malignant neoplasms. Am J Epidemiol. 1997 Aug 1;146(3):223-30. http://aje.oxfordjournals.org/content/146/3/223.full.pdf
6) Cutler GJ et al. Dietary flavonoid intake and risk of cancer in postmenopausal women: the Iowa Women's Health Study. Int J Cancer. 2008 Aug 1;123(3):664-71. http://www.ncbi.nlm.nih.gov/pubmed/18491403
7) Feskanich D et al. Prospective study of fruit and vegetable consumption and risk of lung cancer among men and women. J Natl Cancer Inst. 2000 Nov 15;92(22):1812-23. http://jnci.oxfordjournals.org/content/92/22/1812.full
8) Hirvonen T et al. Flavonol and flavone intake and the risk of cancer in male smokers (Finland). Cancer Causes Control. 2001 Nov;12(9):789-96. http://www.ncbi.nlm.nih.gov/pubmed/11714106
9) Bobe G et al. Flavonoid intake and risk of pancreatic cancer in male smokers (Finland). Cancer Epidemiol Biomarkers Prev. 2008 Mar;17(3):553-62. http://cebp.aacrjournals.org/content/17/3/553.long
10) Vrieling A et al. Fruit and vegetable consumption and pancreatic cancer risk in the European Prospective Investigation into Cancer and Nutrition. Int J Cancer. 2009 Apr 15;124(8):1926-34. http://www.ncbi.nlm.nih.gov/pubmed/19107929

Tuesday, February 21, 2012

Milk does not increase hip fracture risk.

Background: Milk intake has been linked to higher risk of bone fractures. If we google the following combination of search words "milk bone fractures women", we see several titles stating that milk may cause osteoporosis/bone fractures. Or titles with "myths about milk".

Did past studies truly show that milk increases risk of bone fractures?
The links found by google consistently refer to the same scientific article (1). In a 12-year follow-up study, the group of women with the highest intakes of milk, were said to have had a 45% increased risk of hip fracture.

Table 1:

Table 1 shows effects as described in the full text of the article. We see a Relative Risk (RR) of 1.45 (95% CI = 0.87-2.43; P = 0.22) for women consuming 2 or more glasses milk per day. No association was found with risk of forearm fractures.
An effect can be significant in 2 ways:
  • The 95% CI of the RR excludes the "1". This is not the case, because the lower boundary = 0.87 and the upper boundary = 2.43.
  • The P for trend = < 0.05. This is also not the case. The P for trend = 0.22.
In scientific terms, this means that no significant association was found. Or possibly, that a nonsignificantly increased risk was found.

The nonsignificantly 45% increased risk of hip fractures was found for adult milk consumption. But the article also describes effects from teenage milk consumption (see table 2).

Table 2:

We see that women who drank 3 or more glasses of milk per day, during their teenage years, had a nonsignificantly 47% lower risk of hip fractures (RR = 0.53; 95% CI = 0.25-1.16; P for trend = 0.20).

Women with higher intakes of milk during both their teenage years and their adulthood did not have an increased risk op hip fractures (RR = 0.88; 95% CI = 0.58-1.36; no P-value available).

Newer studies: In 2011, a group of researchers looked at all prospective studies (6 studies for women and 3 studies for men) with available data about the relation between milk intake and hip fracture risk (2). Results from the individual studies were grouped together in a so-called meta-analysis. The pooled results showed no association with risk of hip fractures among women (RR = 0.99; 95% CI = 0.96-1.02 per glass of milk per day), but a nonsignificant protective effect among men (RR = 0.91; 95% CI = 0.81-1.01 per glass of milk per day).

Note: Associations found in the newer studies are based on a small amount of cohorts, including a small amount of hip fractures (3.574 fractures among women and 195 fractures among men). More research is needed before any valid conclusions can be drawn.

1) Feskanich et al. Milk, dietary calcium, and bone fractures in women: a 12-year prospective study. Am J Public Health. 1997 Jun;87(6):992-7. http://www.ncbi.nlm.nih.gov/pubmed/9224182
2) Bischoff-Ferrari HA et al. Milk intake and risk of hip fracture in men and women: a meta-analysis of prospective cohort studies. J Bone Miner Res. 2011 Apr;26(4):833-9. doi: 10.1002/jbmr.279. http://www.ncbi.nlm.nih.gov/pubmed/20949604

Monday, February 20, 2012

Saturated fat increases both "bad" LDL-cholesterol and "good" HDL-cholesterol.

Background: In 2010 the USDA published it's last update on the dietary guidelines for Americans. Part D. Section 3 covered the science base for fatty acids and cholesterol (1). The report states that consumption of carbohydrates instead of saturated fat (SFA) will decrease levels of "bad" LDL-cholesterol:

Replacement of SFA with carbohydrates decreased plasma total and LDL cholesterol.

But how will this change in macronutrients influence levels of "good" HDL-cholesterol?

Scientific research: In 2003, a group of Dutch researchers examined the effects on cholesterol of replacing carbohydrates with dietary fats. They searched the scientific literature for all controlled trials on this topic. A total of 60 trials were included in the final meta-analyses.
Results can be seen in the table below:

Effects on serum cholesterol of replacing carbohydrates by saturated fats can be seen in the red rectangle. Both LDL- and HDL- cholesterol increased significantly (P = < 0.001). As a consequence, total cholesterol levels also rose. Noticeable, saturated fat increased HDL-cholesterol to a larger extend than monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA).
The ratio total:HDL-cholesterol did not change with increasing intakes of saturated fats.

1) US Department of Agriculture and US Department of Health and Human Services. Report of the Dietary Guidelines Advisory Committee on the dietary guidelines for Americans, 2010. http://www.cnpp.usda.gov/DGAs2010-DGACReport.htm
2) Mensink RP et al. Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials. Am J Clin Nutr. 2003 May;77(5):1146-55. http://www.ncbi.nlm.nih.gov/pubmed/12716665

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