Potatoes rank as the third most widely consumed crop around the world. In the US, about 35 percent of women of reproductive age (19-50 years) consume potatoes on a daily basis, which accounts for 8 percent of their total daily energy intake. The potential health benefits of the crop have remained debatable, along with their appropriate adjustment in dietary regimes. Nevertheless, the Dietary Guidelines for Americans encourages the consumption of potatoes and includes them in the vegetable food group, and the United Kingdom’s National Dietary Guidelines sort potatoes in the starchy food group.
Despite being rich sources of vitamin C, dietary fiber, potassium and certain phytochemicals, potatoes may have negative effects on glucose metabolism. The latter is attributed to the extensive amounts of rapidly absorbable starch present in the vegetable. This has led epidemiological studies to conclude that higher potato consumption may be associated with increased concentrations of fasting plasma glucose, insulin resistance and an increased risk of type 2 diabetes mellitus.
Potatoes And Risk Of Gestational Diabetes Mellitus (GDM)
Gestational diabetes mellitus (GDM) is a fairly common complication characterized by glucose intolerance triggered with onset or first recognition during pregnancy. GDM not only leads to adverse perinatal outcomes, but is also associated with an increased long-term risk of cardiometabolic complications in both, mother and infant. In order to prevent the latter, the identification of modifiable risk factors contributing to GDM is of crucial importance.
Various studies have demonstrated that foods high in glycemic index could be linked with higher plasma glucose levels as well as higher HbA1c concentrations during pregnancy. Hence, it is quite obvious that a possible association may exist between the consumption of potatoes before pregnancy and an increased risk of developing GDM.
Study: Analyzing Possible Correlation
With the understanding that gestational diabetes could have detrimental health consequences for the mother and infant, along with its possible association with food high in glycemic index, researchers decided to evaluate the association between potato consumption and GDM risk.
Published in the BMJ, the large-scale study was a collaboration of various scientists from the US, belonging to the Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy, National Institutes of Health, Division of Preventive Medicine, Brigham and Women’s Hospital and Harvard Medical School, Department of Nutrition, Harvard TH Chan School of Public Health, Channing Division of Network Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School.
Collecting Data For Evaluation
The study involved 15,632 women from the Nurses’ Health Study II (1991-2001). All women included had no previous records of GDM or any chronic diseases prior to pregnancy. They were given a biennial questionnaire inquiring about disease outcomes, lifestyle behaviors (smoking, medication, etc.) and potato consumption. The participants were asked to report how often they consumed potatoes and in what form (baked, boiled, mashed). This was assessed every four year.
Incident first time GDM was determined from self-reports of physicians and validated medical records. Also, the height and weight of each participant was obtained to calculate their body mass index (BMI), and information about their total physical activity was also ascertained through the questionnaire.
To control possible confounding variables, the overall quality of diet of each participant was derived via a diet score using the alternate healthy eating index 2010 (AHEI-2010). The latter ranges from 0-110 points; a higher score indicates a superior quality diet associated with a lower risk of chronic diseases such as diabetes and cancer.
The data was analyzed by calculating a cumulative average intake of potato consumption before pregnancy for each participant to reduce variation within individuals as well as to represent long-term habitual pre-pregnancy diet. A number of sensitivity analyses using different modeling approaches were performed to ensure the efficacy and reliability of the results.
Potatoes Cause Diabetes: What Results Tell Us
After adjusting for age, dietary and non-dietary factors and parity, it was seen that women with higher potato consumption prior to pregnancy had significantly higher chances of developing GDM.
Over the course of the 10 years of the study, 854 incident cases of GDM were observed among 21,693 singleton pregnancies. Baseline data obtained in 1991 showed that women consuming more potatoes were younger, less likely to be nulliparous, more likely to be smokers, had a higher BMI, were less physically active, consumed greater total energy and ate a low quality diet as represented by the AHEI-2010 dietary pattern score.
Another finding worth considering is the positive correlation observed between the different preparations of potatoes consumed (baked, boiled, mashed, French fries) and the risk of GDM.
Lastly, the association between potato consumption, pregnancy and an increased risk of GDM was robust in various statistical settings. The link remained strong even after adjusting for individual foods related to diabetes, such as fruits, red meat, whole grains and sugars, and after considering the actual continuous proportion of potato consumption rather than an average value.
Possible Explanation Of Findings
Despite lacking details about the underlying mechanisms, researchers believe that their findings are biologically plausible. Potatoes are well-known to have high glycemic index due to the large amounts of readily absorbable starch. This fact explains why consuming large quantities of the vegetable could cause a sharp rise in postprandial (2 hours after a meal) blood glucose concentrations and stimulate oxidative stress and subsequent damage in pancreatic cells that secrete insulin for blood glucose regulation.
Considering the positive correlation observed between the different preparations of potatoes consumed and GDM risk, French fries contain modified fatty acid composition and high amounts of harmful products from the oil they are fried in. These alterations in fried foods have been significantly associated with and implicated in the development of insulin resistance leading to diabetes.
Moreover, the link between French fries and GDM was considerably weakened after further adjusting for BMI, suggesting that the association may be largely due to BMI. This is also quite possible, since frying oil can increase the energy density of foods as well as the risk of obesity.
Another possibility is the relation between high potato consumption, high gestational weight and hence a higher risk of GDM. However, further research into this association needs to be conducted before formulating a link.
Strengths and Potential Limitations Of Study
There are certain factors that substantiate the findings of the study, such as:
Prospective study design with a long-term follow-up of ten years.
Sample size – large number of GDM cases analyzed ensures sufficient statistical accuracy.
Repetitive and comprehensive assessment of various dietary and lifestyle variables which minimizes possible confounders and effect modification.
However, there are certain limitations as well, such as:
Consumption of potatoes and incidences of diabetes were self-reported.
Severity of diabetes was unknown and could not be medically verified.
More than 90 percent of the participants were white American women, putting into question its generalization to other populations.
Despite the relative homogeneity of the sample that reduces confounding due to unmeasured socioeconomic variability, the results cannot be generalized to the entire public.
Since the study is observational, a causal association cannot be assumed.
Analysis And Suggestions
The research concludes that higher pre-pregnancy consumption of potatoes was significantly associated with an increased risk of gestational diabetes mellitus (GDM), even after adjusting for other major risk factors for GDM such as age, family history of diabetes, physical activity, overall diet quality and BMI. These findings corroborate many previous studies that demonstrate a similar association between the consumption of potatoes and type 2 DM. For example, a study where non-pregnant women consumed high amounts of potatoes and French fries were found to have a moderately high risk of type 2 DM after adjusting for age and dietary/non-dietary factors.
Future Interventions Must Include These Extremely Important Aspects
Current dietary guidelines encourage the consumption of high amounts of potatoes as either vegetables or starchy foods. The current findings highlight the need to immediately regulate and revise these suggestions and consider the possible adverse effects of their copious consumption, especially during and between pregnancies.
Substituting two servings of potatoes every week with other vegetables, whole grains or legumes can significantly reduce the risk of GDM by 9 to 12 percent. These alternatives have a lower glycemic index, and are rich in micronutrients and phytochemicals.
Educating women of reproductive age, as well as healthcare professionals regarding essential dietary modifications during pregnancy. In conclusion, researchers suggest that these findings must be confirmed via intervention studies and randomized controlled trials.
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