Obesity prevalence is more than 40% in the United States adult population (1). With many adverse health consequences of obesity, weight loss is the strategy to go for good health.

 

    Phytoestrogens can be one of the strategies to help people to lose weight. Phytoestrogens are compounds derived from plants, which are structurally similar to the primary female sex hormone, estrogen. One of the many benefits phytoestrogens have is to help with weight loss.

 

    Many compounds are known as phytoestrogens, such as isoflavones, stilbene, coumestan, and lignans. Isoflavones are from legumes, especially soybeans. The most common stilbene group is resveratrol, which is abundant in grapes. Coumestans sources include split peas, pinto beans, lima beans, and especially alfalfa and clover sprouts. A good source of lignans is flaxseed (2). This short blog is on soy and its products' effect on body weight.

 

    A randomized controlled clinical trial was conducted in 100 overweight/obese persons (men, n = 20 and women, n = 80) with body mass index (BMI; kg/m2) between 28 and 41, and between the ages of 35 and 65. They received either soy-based meal replacements (treatment) or control meals for 12 weeks. The group using the soy-based diet experienced significantly more reductions in weight (7.0 vs. 2.9 kg), fat mass (4.3 vs. 1.4 kg), and waist circumference (6.0 vs. 2.9 cm) over the 12-week trial than those of the control group. The total cholesterol (22.5 vs. 6.8 mg/dL) and LDL-cholesterol (21.2 vs. 7.1 mg/dL) were also significantly reduced in the treatment group compared to those of the control group (3). Even though 25% of the study subjects dropped off from the study by the end, this study proved that the soy protein meal replacement was an effective treatment for weight loss and fat mass reduction and an effective cholesterol-reducing agent in obese subjects.

 

    Another study also showed that soy-based diets have health benefits in reducing weight and blood lipids. Thirty obese adults (mean body mass index 29-30 kg/m2) were randomized to two groups. The soy-based low-calorie group consumed soy protein as the only protein source, and the traditional low-calorie group consumed two-thirds of animal protein and the rest plant protein in a 1200 kcal/day diet for a total of 8 weeks.  Bodyweight, body mass index, body fat percentage, and waist circumference significantly decreased in both groups. The decrease in body fat percentage in the soy group (2.2%) was more than that in the traditional group (1.4%). Serum total cholesterol concentrations, low-density lipoprotein cholesterol concentrations, and liver function parameters decreased in the soy-based group and were significantly different from measurements in the traditional group (P < 0.05) (4). This study showed that soy-based low-calorie diets significantly decreased serum total cholesterol and low-density lipoprotein cholesterol concentrations and had a larger effect on reducing body fat percentage than traditional low-calorie diets.

 

    A group of scientists compared the anti-obesity effect of doenjang, a fermented soybean paste, with nonfermented soybeans in rats. Steamed soybeans and doenjang (steamed soybeans fermented and aged for 10  months) were freeze-dried. Rats were fed basal (BA) (5% fat), high fat (30% fat), high fat+steamed soybeans (SOY), or high fat+doenjang (DJ) diet ad libitum for 8 weeks. high-fat diet significantly increased body weight gain, liver weight, hepatic triglyceride and cholesterol levels, and epididymal fat pad weight compared with BA. Compared with the high-fat diet, body weight gain and hepatic triglyceride and cholesterol levels were significantly lower in SOY and DJ groups, but they were not statistically significantly different from each other. DJ significantly reduced visceral fat weight and epididymal adipocyte size compared with those of the high-fat diet, whereas SOY resulted in a mild reduction without significant difference. The authors suggested that doenjang, the fermented soybean product, was more effective than soybean for preventing diet-induced visceral fat accumulation, which may be due in part to the higher content of aglycone isoflavones in doenjang (5).

 

    Other studies in animals have shown the protective effect of phytoestrogens on the risk of obesity in estrogen-deficient mice. In a group of mice given a diet high in phytoestrogens there was a decrease in the amount of food intake and increase weight loss compared to those of the control group. One of the effects of estrogen is appetite suppression. Because phytoestrogens have a structure similar to estrogen and can bind to estrogen receptors, phytoestrogens also have appetite-suppressing properties (6).

 

    One study investigated the combinatory effects of an isoflavone (phytoestrogen in soy) -rich diet and exercise on fat mass and lipid metabolism in ovariectomized rats. The female rats were sedentary, performed an intense treadmill uphill running, received isoflavones, or a combination of isoflavones + running after ovariectomy (7). The bodyweight of ovariectomized rats gained the most.  The largest visceral fat mass, adipocyte size, and serum leptin level were observed in ovariectomized rats. Interestingly, the food consumption of ovariectomized rats was not more than the rats in other groups. In trained rats, visceral fat mass, adipocyte size, and leptin levels were significantly reduced in Sham and ovariectomized rats. In ovariectomized rats, an isoflavone -rich diet reduced leptin serum levels but showed no significant effects on fat mass and adipocyte size. A combination of isoflavone + running did not result in additive effects (7).

 

    The results demonstrated that both the exercising and isoflavones affected fat mass and fatty acid metabolism in ovariectomized rats. A soy-rich diet alone may have some preventive effect on weight gain associated with estrogen deficiency, but exercising/training seemed to have a higher impact than isoflavone (phytoestrogen) exposure in regulating gene expression in adipose tissue and body fat mass. The take-home message is that it may need a combination of exercising and a soy-rich diet for the prevention of obesity.

 

    Menopause is associated with an increase in body weight. Phytoestrogens such as ones found in soy products may benefit weight gain prevention and help with weight loss, which may be especially beneficial to women with declining estrogen levels.

 

References:

1. CDC: https://www.cdc.gov/obesity/data/adult.html.

2. Desmawati, D., & Sulastri, D. A Phytoestrogens and Their Health Effect. Open Access Macedonian Journal of Medical Sciences. 2019; 7(3) : 495–499.

3. Allison DB, Gadbury G, Schwartz LG, Murugesan R, Kraker JL, Heshka S, Fontaine, KR, Heymsfield, SB. A novel soy-based meal replacement formula for weight loss among obese individuals: a randomized controlled clinical trial. European journal of clinical nutrition. 2003; 57(4):514.

4. Liao, F.-H., Shieh, M.-J., Yang, S.-C., Lin, S.-H., & Chien, Y.-W. (2007). Effectiveness of a soy-based compared with a traditional low-calorie diet on weight loss and lipid levels in overweight adults. Nutrition. 2007; 23(7-8): 551–556.

5. Kwak, C. S., Park, S. C., & Song, K. Y. Doenjang, a Fermented Soybean Paste, Decreased Visceral Fat Accumulation and Adipocyte Size in Rats Fed with High Fat Diet More Effectively Than Nonfermented Soybeans. Journal of Medicinal Food. 2012. 15(1): 1–9.

6. Tolba EA-EHT. Dietary phytoestrogens reduce the leptin level in ovariectomized female rats. Cellulose. 2013; 1(1.10):0.17.

7. Zheng, W., Rogoschin, J., Niehoff, A., Oden, K., Kulling, S. E., Xie, M., & Diel, P. Combinatory effects of phytoestrogens and exercise on body fat mass and lipid metabolism in ovariectomized female rats. The Journal of Steroid Biochemistry and Molecular Biology. 2018, 178:73–81.