Abstract
Summary Mean serum insulin-like growth factor-I was 9% lower in 233 vegan men than in 226 meat-eaters and 237 vegetarians (P = 0.002). Vegans had higher testosterone levels than vegetarians and meat-eaters, but this was offset by higher sex hormone binding globulin, and there were no differences between diet groups in free testosterone, androstanediol glucuronide or luteinizing hormone. 2000 Cancer Research Campaign
Generated Summary
This cross-sectional study investigated the serum concentrations of sex hormones and related proteins in 696 men, categorized into three dietary groups: meat-eaters, vegetarians, and vegans. The study aimed to assess the influence of diet on hormone levels, particularly focusing on insulin-like growth factor-I (IGF-I), sex hormone-binding globulin (SHBG), testosterone (T), and other related factors. The study was conducted as part of the European Prospective Investigation into Cancer and Nutrition (EPIC) study in Oxford, UK. Data collection involved blood sample analysis for hormone levels and the use of a semi-quantitative food frequency questionnaire to estimate nutrient intakes. The study hypothesized that dietary variations, particularly a vegan diet, would be associated with lower levels of androgens and IGF-I, which are linked to prostate cancer risk. The study design involved recruiting participants and collecting detailed information on their dietary habits, medical history, and lifestyle factors to analyze the relationships between diet and hormone concentrations. Statistical analyses were performed to compare hormone levels and nutrient intakes across the dietary groups, adjusting for potential confounding factors like age and body mass index (BMI).
Key Findings & Statistics
- The study included 226 meat-eaters, 237 vegetarians, and 233 vegans.
- Vegans had a significantly lower mean serum insulin-like growth factor-I (IGF-I) level than meat-eaters and vegetarians (P = 0.002).
- Vegans had higher testosterone levels than vegetarians and meat-eaters.
- There were no differences in free testosterone, androstanediol glucuronide, or luteinizing hormone between diet groups.
- The mean age for meat-eaters was 52.8 years, for vegetarians 46.3 years, and for vegans 42.9 years (P < 0.0001).
- The mean weight for meat-eaters was 82.4 kg, for vegetarians 74.4 kg, and for vegans 71.8 kg (P < 0.0001).
- Mean BMI was 26.1 for meat-eaters, 23.4 for vegetarians, and 22.7 for vegans (P < 0.0001).
- Energy intake was 10.3 MJ for meat-eaters, 8.88 MJ for vegetarians, and 8.08 MJ for vegans (P < 0.0001).
- Protein intake (% energy) was 16.6% for meat-eaters, 13.2% for vegetarians, and 12.7% for vegans (P < 0.0001).
- Total fat intake (% energy) was 34.0% for meat-eaters, 31.0% for vegetarians, and 29.9% for vegans (P < 0.0001).
- Saturated fatty acids intake (% energy) was 11.8% for meat-eaters, 8.71% for vegetarians, and 4.87% for vegans (P < 0.0001).
- Polyunsaturated fatty acids intake (% energy) was 5.39% for meat-eaters, 6.12% for vegetarians, and 8.17% for vegans (P < 0.0001).
- Cholesterol intake (mg/day) was 327 for meat-eaters, 112 for vegetarians, and 20.8 for vegans (P < 0.0001).
- Vegans had 9% lower IGF-I levels compared to meat-eaters (P < 0.01) and 8% lower compared to vegetarians (P < 0.01).
- After adjusting for BMI, vegans still showed lower IGF-I levels, with similar differences.
- SHBG levels in vegans were 16% higher than in meat-eaters (P < 0.0001) and 12% higher than in vegetarians (P = 0.0008) before adjusting for BMI.
- After adjusting for BMI, the difference in SHBG levels between vegans and meat-eaters reduced to 6% (P = 0.02), and between vegans and vegetarians to 10% (P = 0.004).
- Vegans had 13% higher testosterone (T) concentrations than meat-eaters (P = 0.0001) and 8% higher than vegetarians (P = 0.001).
- Adjusting for BMI reduced these differences to 6% (P = 0.07) and 7% (P = 0.02), respectively.
- After adjusting for SHBG, the differences in T concentrations were substantially reduced.
- Plasma total cholesterol was 17% lower in vegans compared to meat-eaters (P < 0.0001) and 10% lower compared to vegetarians (P < 0.0001).
Other Important Findings
- Vegans had lower weight and BMI than meat-eaters.
- Vegetarians and vegans had lower intakes of energy, protein, total fat, saturated and monounsaturated fatty acids, and alcohol (as % energy) compared to meat-eaters.
- Vegans had higher intakes of polyunsaturated fatty acids (% energy), polyunsaturated:saturated fatty acid ratio, and non-starch polysaccharides than meat-eaters.
- No significant differences in free testosterone, androstanediol glucuronide, or luteinizing hormone were found between dietary groups.
- The study found substantial differences in plasma total cholesterol, with vegans having significantly lower mean values than meat-eaters and vegetarians.
Limitations Noted in the Document
- The study is cross-sectional, limiting the ability to establish causal relationships between diet and hormone levels.
- Self-reported dietary data may be subject to recall bias and inaccuracies.
- The study’s focus on men in the Oxford, UK area may limit the generalizability of the findings to other populations.
- The study did not include detailed information on the specific types of vegetarian diets (e.g., lacto-ovo) and the potential impact on results.
- The exclusion of participants with cancer or those taking medication that influences hormone levels may limit the representativeness of the sample.
- The study design did not account for all potential confounding factors, though adjustments were made for age, smoking status, and other variables.
- The study’s focus on hormone levels provides only an indirect measure of prostate cancer risk.
- The lack of longitudinal data prevents an assessment of the long-term effects of the observed hormonal differences.
Conclusion
The study findings indicate that a vegan diet is associated with lower levels of insulin-like growth factor-I (IGF-I) and higher levels of sex hormone-binding globulin (SHBG) and testosterone compared to meat-eaters and vegetarians. These differences in hormone levels may be significant in the context of prostate cancer risk, given the potential role of IGF-I in stimulating cell proliferation and the influence of androgens. The results suggest that dietary choices can influence circulating hormone profiles, which could have implications for disease risk. As the authors state, “The significant 9% lower IGF-I concentration among vegan men compared to meat-eaters has not been reported before.” The lower levels of cholesterol observed in the vegan group support previous research and highlight the impact of diet on lipid metabolism. However, the cross-sectional nature of the study means that it can’t demonstrate a cause-and-effect relationship. Also, in relation to prostate cancer, “Prospective data have shown that vegetarians do not have significantly lower prostate cancer mortality rates than comparable non-vegetarians” but there is not sufficient data on vegan men. Further research is needed to confirm these findings. The authors suggest “Prospective data have shown that vegetarians do not have significantly lower prostate cancer mortality rates than comparable non-vegetarians.”.