Effects of Low-Fat Diet on Cancer, Cardiovascular Disease, and Diabetes in Postmenopausal Women

by | Sep 23, 2019 | 2019, Cancer, Cardiovascular Health, Diabetes, Menopause, Women's Health

Written by Angeline A. De Leon, Staff Writer. Reduction in dietary fat with a commensurate increase in carbohydrate, with vegetable, fruit, and grain increases, over a 19.6 year median follow-up revealed a significant reduction in breast cancer, diabetes requiring insulin, estrogen receptor positive, progesterone receptor negative breast cancer, and coronary heart disease.

Referring to the ratio of fats, carbohydrates, and proteins, macronutrient balance remains one of the most controversial topics in nutrition research. Observational literature presents mixed findings, with epidemiological evidence from one global study, for example, reporting higher total mortality in relation to low-fat, high-carbohydrate diets 1, and another cohort study suggesting that mortality risk is highest for low-carbohydrate diets, elevated for high-carbohydrate diets, and lowest only in diets involving about 50% of energy from carbohydrates 2. In line with these variable findings, a 2018 review study suggests that protective effects against chronic disease are achievable with a broad range of ratios of carbohydrates to fats 3. The Women’s Health Initiative (WHI) Dietary Modification (DM) Trial was conducted in the mid-1990’s in an effort to elucidate the effects of a low-fat dietary pattern (involving concomitant increase in intake of vegetables, fruits, and grains) on cancer 4,5, coronary heart disease (CHD) 6, diabetes 7, and total mortality (4) in postmenopausal women. In an updated overview of the long-term health outcomes associated with the WHI DM trial, a 2019 study 8 published in the Journal of Nutrition and Disease reports on the relationship between a low-fat diet and risk of breast cancer, colorectal cancer, CHD, and other clinical outcomes over a follow-up period of nearly 20 years.

A total of 48,835 postmenopausal women (aged 50 to 79 years) with dietary fat intake estimated to be ≥ 32% of total energy intake (estimated by food frequency questionnaire, FFQ) were enrolled in a 1-year randomized controlled trial conducted across 40 clinical centers throughout the U.S. Forty % of subjects were randomized to a low-fat dietary pattern intervention (involving a reduction in fat from about 35% of energy at baseline to 20%, along with increased intake of fruits and vegetables to 5 servings daily and increased intake of grains to 6 servings daily), and 60% were assigned to a usual-diet comparison group. The FFQ was administered at baseline, 1 year, and about every 3 years following the intervention period, and blood samples were collected from a subsample of participants to analyze nutritional variables. Incidence rates, disease outcomes, and mortality data for total cancer, total CHD, total stroke, total cardiovascular disease (CVD), and diabetes were pulled from the U.S. National Cancer Institute and the National Death Index.

At the 8.5-year median follow-up period, the intervention group demonstrated a fat intake of total energy that was about 11% lower than the control group, as well as about a 10% relative increase in carbohydrate intake (p < 0.001 for both). Overall intake of fruits, vegetables, and grains was also higher for the low-fat group, relative to controls (p < 0.001 for all). Over the 19.6-year median follow-up period, a significant reduction was observed in composite outcome of breast cancer followed by death from any cause (Hazard Ratio = 0.84, 95% Confidence Interval: 0.74 to 0.96, p = 0.01) and for diabetes requiring insulin (HR = 0.87, 95% CI: 0.77 to 0.98, p = 0.02). There was also a significant reduction in incidence of estrogen receptor positive, progesterone receptor negative breast cancer (HR = 0.77, 95% CI = 0.64 to 0.94), diabetes requiring oral agents followed by death (HR = 0.90, 95% CI: 0.82 to 1.00), and diabetes requiring insulin followed by death (HR = 0.65, 95% CI: 0.52 to 0.82) over the longer-term follow-up. Finally, exploratory analyses showed a significant reduction in CHD incidence (HR = 0.70, 95% CI: 0.56 to 0.87, p = 0.03) among baseline normotensive participants, compared to hypertensive participants, over cumulative follow-up.

The present study provides the most recent update to the WHI DM trial, indicating that over a follow-up period of almost 20 years, a change in dietary pattern characterized by lower fat intake and higher intake of fruits, vegetables, and grains is associated with key benefits in breast cancer, CHD, and diabetes in postmenopausal women. Although no significant differences were evident for invasive breast cancer or colorectal cancer or secondary CHD, overall findings are consistent with previous research supporting the protective effects of a lower-fat diet against chronic disease (1). In the current study, specifically, the replacement of fats by carbohydrates appears to be of benefit. Strengths of the study include its large sample size and long-term follow-up period, while potential weaknesses relate to the trial’s primary reliance on self-report measures (FFQ) and its lack of specificity in measuring fat reduction (e.g., total vs. saturated or saturated).

Source: Prentice RL, Aragaki AK, Howard BV, et al. Low-fat dietary pattern among postmenopausal women influences long-term cancer, cardiovascular disease, and diabetes outcomes. The Journal of Nutrition and Disease. 2019; 149: 1565-1574. DOI: 10.1093/jn/nxz107.

© American Society for Nutrition 2019. All rights reserved. This is an Open Access article distributed under the terms of the Creative Commons AttributionNon-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/)

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Posted September 23, 2019.

Angeline A. De Leon, MA, graduated from the University of Illinois at Urbana-Champaign in 2010, completing a bachelor’s degree in psychology, with a concentration in neuroscience. She received her master’s degree from The Ohio State University in 2013, where she studied clinical neuroscience within an integrative health program. Her specialized area of research involves the complementary use of neuroimaging and neuropsychology-based methodologies to examine how lifestyle factors, such as physical activity and meditation, can influence brain plasticity and enhance overall connectivity.

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