Ahmed El-sohemy | University of Toronto (original) (raw)

Papers by Ahmed El-sohemy

Cancer Epidemiology Biomarkers & Prevention, 2010

Epidemiologic evidence supports a role for vitamin D in colorectal cancer (CRC) risk. Variants in... more Epidemiologic evidence supports a role for vitamin D in colorectal cancer (CRC) risk. Variants in vitamin D-related genes might modify the association between vitamin D levels and CRC risk. In this analysis, we did a comprehensive evaluation of common variants in the vitamin D receptor (VDR) and the vitamin D-binding protein (GC; group-specific component) genes using a population-based case-unaffected sibling control design that included 1,750 sibships recruited into the Colon Cancer Family Registry. We also evaluated whether any associations differed by calcium supplement use, family history of CRC, or tumor characteristics. Heterogeneity by calcium and vitamin D intake was evaluated for a subset of 585 cases and 837 sibling controls who completed a detailed food frequency questionnaire. Age-and sex-adjusted associations were estimated using conditional logistic regression. Overall, we did not find evidence for an association between any singlenucleotide polymorphism (SNP) in VDR or GC and risk for CRC (range of unadjusted P values 0.01-0.98 for VDR and 0.07-0.95 for GC). None of these associations was significant after adjustment for multiple comparisons. We also found no evidence that calcium or vitamin D intake (food and supplement) from the food frequency questionnaire modified the association estimates between VDR and GC SNPs and CRC. We did observe associations between SNPs in GC and microsatellite unstable CRC, although these results should be confirmed in additional studies. Overall, our results do not provide evidence for a role of common genetic variants in VDR or GC in susceptibility to CRC. Cancer Epidemiol Biomarkers Prev; 19(2); 525-36.

Forum of Nutrition, 2007

Food preferences are influenced by a number of factors such as personal experiences, cultural ada... more Food preferences are influenced by a number of factors such as personal experiences, cultural adaptations and perceived health benefits. Taste, however, is the most important detenninant of how much a food is liked or disliked. Based on the response to bitter-tasting compounds such as phenylthiocarbamide (PTC) or 6-n-propylthiouracil (PROP). individuals can be classified as supertasters, tasters or nontasters. Sensitivity to bitter-tasting compounds is a genetic trait that has been recognized for more than 70 years. Genetic differences in bitter taste perception may account for individual differences in food preferences. Other factors such as age, sex and ethnicity may also modify the response to bitter-tasting compounds. There are several members of the TAS2R receptor gene family that encode taste receptors on the tongue, and genetic polymorphisms of TAS2R38 have been associated with marked differences in the perception of PTC and PROP. However, the association between TAS2R38 genotypes and aversion to bitter-tasting foods is not clear. Single nucleotide polymorphisms in other taste receptor genes have recently been identified, but their role in bitter taste perception is not known. Establishing a genetic basis for food likes/dislikes may explain, in part, some ofthe inconsistencies among epidemiologic studies relating diet to risk of chronic diseases. Identifying populations with preferences for particular flavors or foods may lead to the development of novel food products targeted to specific genotypes or ethnic populations.

Background: Cruciferous vegetables are a major dietary source of isothiocyanatesthatmayprotectaga... more Background: Cruciferous vegetables are a major dietary source of isothiocyanatesthatmayprotectagainstcoronaryheartdisease.Iso- thiocyanates induce glutathione S-transferases (GSTs), polymor- phic genes that code for enzymes that conjugate isothiocyanates, as well as mutagens and reactive oxygen species, to make them more readily excretable. Objective: The objective of the study was to determine whether GST genotypes modify the association between cruciferous vegeta- ble intake and

The Journal of nutrition, Jan 13, 2015

Choline deficiency during pregnancy can lead to adverse birth outcomes, including impaired neurod... more Choline deficiency during pregnancy can lead to adverse birth outcomes, including impaired neurodevelopment and birth defects. Genetic variants of choline and one-carbon metabolism may also influence birth outcomes by altering plasma choline concentrations. The effects of maternal ad libitum choline intake during pregnancy and fetal genetic variants on maternal and cord concentrations of choline and its metabolites are unknown. This prospective study sought to assess the effect of 1) maternal dietary choline intake on maternal and cord plasma concentrations of choline and its metabolites, and 2) fetal genetic polymorphisms on cord plasma concentrations. The dietary choline intake of 368 pregnant Canadian women was assessed in early (0-16 wk) and late (23-37 wk) pregnancy with the use of a food frequency questionnaire. Plasma concentrations of free choline and its metabolites were measured in maternal samples at recruitment and delivery, and in the cord blood. Ten fetal genetic varia...

Journal of Caffeine Research, 2011

... 30. Ainsworth BE, Haskell WL, Leon AS, et al. Compendium of physical activities: classificati... more ... 30. Ainsworth BE, Haskell WL, Leon AS, et al. Compendium of physical activities: classification of energy costs of human physical activities. ... 41. Vistisen K, Poulsen HE, Loft S. Foreign compound metabolism capacity in man measured from metabolites of dietary caffeine. ...

Journal of Caffeine Research, 2013

Erdman/Present Knowledge in Nutrition, 2012

The American journal of clinical nutrition, 2007

Caffeine is the most widely consumed stimulant in the world, and individual differences in respon... more Caffeine is the most widely consumed stimulant in the world, and individual differences in response to its stimulating effects may explain some of the variability in caffeine consumption within a population. We examined whether genetic variability in caffeine metabolism [cytochrome P450 1A2 (CYP1A2) -163A-->C] or the main target of caffeine action in the nervous system [adenosine A(2A) receptor (ADORA2A) 1083C-->T] is associated with habitual caffeine consumption. Subjects (n=2735) were participants from a study of gene-diet interactions and risk of myocardial infarction who did not have a history of hypertension. Genotype frequencies were examined among persons who were categorized according to their self-reported daily caffeine intake, as assessed with a validated food-frequency questionnaire. The ADORA2A, but not the CYP1A2, genotype was associated with different amounts of caffeine intake. Compared with persons consuming <100 mg caffeine/d, the odds ratios for having th...

Nutrition & Metabolism, 2015

Background: There is great interest in the relationship between polyunsaturated fatty acids and h... more Background: There is great interest in the relationship between polyunsaturated fatty acids and health. Yet, the combinatory effect of factors such as sex, ethnicity, genetic polymorphisms and hormonal contraceptives (HC) on the concentrations of these fatty acids is unknown. Therefore, we sought to determine the effects of FADS polymorphisms, and HC use in females, on aggregate desaturase indices (ADI), and plasma docosahexaenoic acid (DHA) concentrations in Caucasian and East Asian males and females. Methods: Fasting plasma samples were collected from subjects (Caucasian males: 113 and females: 298; East Asian males: 98 and females: 277) from the Toronto Nutrigenomics and Health Study. Fatty acid concentrations were measured by gas chromatography. ADI were estimated by dividing concentrations of arachidonic acid by linoleic acid (n-6 ADI) and eicosapentaenoic acid (EPA) by α-linolenic acid (n-3 ADI). [DHA/EPA] desaturase index was used to determine effects of FADS2 polymorphisms and HC use on EPA conversion to DHA. Results: In Caucasians, associations between n-6 ADI and multiple SNP (in females) withstood multiple testing. In East Asian females, 5 SNP-n-6 ADI associations (FADS2 rs174602, rs174626, rs2072114, rs2845573, and rs2851682) withstood multiple testing. One FADS2 SNP was associated with altered [DHA/EPA] desaturase index in Caucasian females only (rs174576, p < 0.0001). HC use had a significant effect on DHA concentrations in Caucasian females only (P < 0.0001). Conclusions: We demonstrate ethnic-and sex-specific effects of FADS polymorphisms on desaturase indices, and ethnic-specific effect of HC use on plasma DHA concentrations.

Carcinogenesis

The effects of dietary cholesterol and oxidized cholesterol on mammary tumor development were exa... more The effects of dietary cholesterol and oxidized cholesterol on mammary tumor development were examined in female Sprague-Dawley rats exposed to the carcinogen N-methyl-N-nitrosourea (MNU). Animals were administered 50 mg/kg MNU at 50 days of age and fed either a control (AIN-76) diet or the control diet supplemented with 0.3% cholesterol or 0.3% oxidized cholesterol for up to 26 weeks. The oxidized cholesterol was prepared by heating cholesterol at 110 degrees C for 48 h. Gas chromatographic analysis of the oxidized cholesterol revealed a 2% yield of oxidation products in addition to a large amount of unchanged cholesterol (> 96%). Tumor incidence in the cholesterol group (67%) was significantly lower than in the control group (96%, P < 0.05), but the oxidized cholesterol group (79%) was not significantly different from the control or cholesterol groups. Average number of tumors per animal was lower in the cholesterol group (1.5) than in the control (2.8) or oxidized cholester...

Biologics : targets & therapy, 2011

The incidence of type 2 diabetes mellitus (T2DM) is increasing worldwide, and certain population ... more The incidence of type 2 diabetes mellitus (T2DM) is increasing worldwide, and certain population subgroups are especially vulnerable to the disease. To reduce T2DM risk and progression at the population level, preventative strategies are needed that can be implemented on a population-wide scale with minimal cost and effort. Chronic low-grade inflammation resulting from oxidative stress and imbalances in the innate immune system has been associated with obesity, metabolic syndrome, and insulin resistance - critical stages in the development and progression of T2DM. Therefore, inflammation may play a causal role in the pathogenesis of T2DM, and reducing it via modulation of oxidative stress and the innate immune response could lead to a status of improved insulin sensitivity and delayed disease onset. Dietary supplementation with anti-inflammatory and antioxidant nutritional factors, such as micronutrients, might present a novel strategy toward the prevention and control of T2DM at th...

PloS one, 2014

Proponents of consumer genetic tests claim that the information can positively impact health beha... more Proponents of consumer genetic tests claim that the information can positively impact health behaviors and aid in chronic disease prevention. However, the effects of disclosing genetic information on dietary intake behavior are not clear. A double-blinded, parallel group, 2:1 online randomized controlled trial was conducted to determine the short- and long-term effects of disclosing nutrition-related genetic information for personalized nutrition on dietary intakes of caffeine, vitamin C, added sugars, and sodium. Participants were healthy men and women aged 20-35 years (n = 138). The intervention group (n = 92) received personalized DNA-based dietary advice for 12-months and the control group (n = 46) received general dietary recommendations with no genetic information for 12-months. Food frequency questionnaires were collected at baseline and 3- and 12-months after the intervention to assess dietary intakes. General linear models were used to compare changes in intakes between tho...

Genes & nutrition, 2012

Personal genetic information has become increasingly accessible to the public as a result of dire... more Personal genetic information has become increasingly accessible to the public as a result of direct-to-consumer (DTC) genetic tests; however, concerns have been raised over their value and potential risks. We compared the effects of providing genotype-based dietary advice with general recommendations on behavioral outcomes using a randomized controlled study. Participants were men and women from the Toronto Nutrigenomics and Health Study between the ages of 20-35 years (n = 149) who completed a survey to assess their awareness of DTC genetic tests and nutrigenomics, as well as potential motivations for undergoing genetic testing. Participants were then randomized into an intervention (I) or control (C) group and were given either genotype-based personalized dietary advice or general dietary advice, respectively. A second survey was administered to assess the participants' opinions of the dietary reports they received. A greater proportion of participants in the intervention grou...

Experimental biology and medicine (Maywood, N.J.), 2007

Mixed isomers of conjugated linoleic acid (CLA) have been shown to have variable effects on bone ... more Mixed isomers of conjugated linoleic acid (CLA) have been shown to have variable effects on bone formation and resorption in animals. The variable effects of CLA on bone physiology may be due to the different isomers present in common commercial preparations of CLA, and the effects of the predominant individual isomers (9cis,11trans and 10trans,12cis CLA) are not clear. The objective of this study was to determine the effects of individual and mixed isomers of CLA on mineralized bone nodule formation and alkaline phosphatase (ALP) activity in vitro using long-term cultures of SaOS-2 cells. Mineralized bone nodules were stained using the von Kossa method, and ALP activity in cell lysates was measured as a marker of early osteoblast differentiation. The 9cis,11trans isomer increased the number (~4- to 11-fold) and size (~2- to 5-fold) of mineralized bone nodules from 25 to 100 microM, but the 10trans,12cis isomer did not. The increase in mineralized bone nodule formation by 9cis,11tra...

Rheumatology international, 2006

Catalase (CAT) and peroxisome proliferator activated receptor-gamma2 (PPARgamma2) are important r... more Catalase (CAT) and peroxisome proliferator activated receptor-gamma2 (PPARgamma2) are important regulators of oxidative stress and inflammation, and may contribute to the development of rheumatoid arthritis (RA). We investigated the association between CAT and PPARgamma2 genotypes and risk and severity of RA using 474 cases and 400 controls. Genotyping for the -262C-->T polymorphism of CAT and the Pro12Ala polymorphism of PPARgamma2 was performed by PCR-RFLP analysis. Severity of RA was assessed by the anatomical stage according to Steinbrocker, and a Korean language version of a Health Assessment Questionnaire (KHAQ). No association was observed between CAT and PPARgamma2 genotypes and risk of RA. Our results suggest that genetic polymorphisms of CAT and PPARgamma2 do not play a significant role in the susceptibility to RA among Koreans.

The American journal of clinical nutrition, 2002

Plasma and adipose tissue concentrations of carotenoids are thought to reflect short- and long-te... more Plasma and adipose tissue concentrations of carotenoids are thought to reflect short- and long-term intakes of carotenoids, respectively. The ability of adipose tissue carotenoid concentrations to reflect dietary intake in population studies is unknown. We examined the relation between intakes of the major dietary carotenoids and their concentrations in plasma and adipose tissue. A blood sample and an adipose tissue biopsy sample were collected from 115 women and 344 men in Costa Rica after they had fasted overnight, and a dietary interview based on a 135-item food-frequency questionnaire was administered. After carotenoid intake was adjusted for total energy intake and plasma concentrations were adjusted for HDL-, LDL-, and VLDL-cholesterol concentrations, we calculated partial Spearman correlation coefficients that were adjusted for age, sex, smoking, and body mass index. In women, the correlations (r) between intakes and concentrations of alpha-carotene, beta-carotene, beta-crypt...

Epidemiology (Cambridge, Mass.), 2002

Gamma-tocopherol, the most abundant form of dietary vitamin E, may lower the risk of coronary hea... more Gamma-tocopherol, the most abundant form of dietary vitamin E, may lower the risk of coronary heart disease. We investigated whether dietary and adipose tissue gamma-tocopherol are associated with myocardial infarction (MI) in 475 survivors of a first MI and 479 controls from a population-based study carried out between 1994 and 1998 in Costa Rica. Dietary intake was assessed with a validated food-frequency questionnaire and an adipose tissue sample. Conditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (CI). Subjects in the highest quintile of dietary gamma-tocopherol had a lower risk of MI compared with those in the lowest quintile (OR = 0.76; 95% CI = 0.50-1.17, P = 0.02 for trend). This trend was no longer statistically substantial in multivariate analysis (P = 0.44). A weak association was found for adipose tissue gamma-tocopherol in univariate (OR = 1.46; 95% CI = 0.94-2.27) and multivariate (OR = 1.31; 95% CI = 0.62-2.76) models. ...

Advances in experimental medicine and biology, 1999

... Badawi AF, el-Sohemy A, Stephen LL, Ghoshal AK, Archer MC. Laboratory of Pharmacogenetics, Cl... more ... Badawi AF, el-Sohemy A, Stephen LL, Ghoshal AK, Archer MC. Laboratory of Pharmacogenetics, Clinical Pharmacology, Atlantic Veterinary College, Charlottetown, Prince Edward Island, Canada. PMID: 10667319 [PubMed - indexed for MEDLINE]. MeSH Terms: ...

Flavour, 2012

Background: Cilantro, the leaf of the Coriandrum sativum plant, is an herb that is widely consume... more Background: Cilantro, the leaf of the Coriandrum sativum plant, is an herb that is widely consumed globally and has purported health benefits ranging from antibacterial to anticancer activities. Some individuals report an extreme dislike for cilantro, and this may explain the different cilantro consumption habits between populations. However, the prevalence of cilantro dislike has not previously been reported in any population. The objective of this study was to determine the prevalence of cilantro dislike among different ethnocultural groups from a population of young adults living in Canada. Subjects (n = 1,639) between the ages of 20 and 29 years were participants of the Toronto Nutrigenomics and Health Study. Individuals rated their preference for cilantro on a 9-point scale from 'dislike extremely' to 'like extremely'. Subjects also had the option to select 'have not tried' or 'would not try'. Subjects who selected 1 to 4 were classified as disliking cilantro. Results: The prevalence of dislike ranged from 3 to 21%. The proportion of subjects classified as disliking cilantro was 21% for East Asians, 17% for Caucasians, 14% for those of African descent, 7% for South Asians, 4% for Hispanics, and 3% for Middle Eastern subjects. Conclusions: These findings show that the prevalence of cilantro dislike differs widely between various ethnocultural groups.

Cancer Epidemiology Biomarkers & Prevention, 2007

We have recently reported that, among BRCA1 mutation carriers, the consumption of caffeinated cof... more We have recently reported that, among BRCA1 mutation carriers, the consumption of caffeinated coffee was associated with a significant reduction in breast cancer risk. Because the metabolism of caffeine is primarily by CYP1A2, we examined whether or not the CYP1A2 genotype modifies the association between a history of coffee consumption and the risk of breast cancer. A common A to C polymorphism in the CYP1A2 gene is associated with decreased enzyme inducibility and impaired caffeine metabolism. Information regarding coffee consumption habits and the CYP1A2 genotype was available for 411 BRCA1 mutation carriers (170 cases and 241 controls). We estimated the odds ratios (ORs) and 95% confidence intervals (95% CIs) for breast cancer associated with the CYP1A2 genotype and a history of coffee consumption before age 35, adjusting for potential confounders. The CYP1A2 genotype did not affect breast cancer risk. Among women with at least one variant C allele (AC or CC), those who consumed coffee had a 64% reduction in breast cancer risk, compared with women who never consumed coffee (OR, 0.36; 95% CI, 0.18-0.73). A significant protective effect of coffee consumption was not observed among women with the CYP1A2 AA genotype (OR, 0.93; 95% CI, 0.49-1.77). Similar results were obtained when the analysis was restricted to caffeinated coffee. This study suggests that caffeine protects against breast cancer in women with a BRCA1 mutation and illustrates the importance of integrating individual genetic variability when assessing diet-disease associations. (Cancer Epidemiol Biomarkers Prev 2007;16(5):912 -6) Cancer Epidemiol Biomarkers Prev 2007;16(5).