An alarming trend is taking place in the United States today that's affecting the health and wellbeing of our children. The rate at which our children are going through puberty has increased significantly between 1997 and 2010. Before the 20th century, the average age of puberty in girls was 16 or 17. The age of menarche has declined over the past 100 years. Today, approximately 16% of young girls are reaching puberty by the time they have their 7th birthday, and roughly 30% by the time they turn 8. Doctor Joel Fuhrman attributes the decline in age in Western countries to an increased consumption of animal products and calorie intake. He believes early puberty is a sign of early aging. In his article Girls are Reaching Puberty Earlier Than Ever, Dr. Fuhrman writes, "The normal, healthy age at menarche under conditions of excellent nutrition without caloric excess, would probably fall somewhere between 15 and 18. But today in the U.S., about half of girls begin developing breasts before age 10, and the average age at menarche is less than 12 and still declining."
Dr. John McDougall cites evidence showing the onset of sexual maturity has "decreased at a rate of about 2 to 6 months per decade." He adds, "Similar changes have been seen in other western European countries over the past 160 years. The slowest onset of maturity, with a mean age of menarche of 18-19 years, was observed in women of Papua New Guinea in the 1960s - a time when the people ate a nearly vegetarian, very low-fat diet."
A recent study from the University of North Carolina at Chapel Hill published in the medical journal Pediatrics reported, "At age 3 years, 3% of African-American and 1% of white girls showed breast and/or pubic hair development, with proportions increasing to 27.2% and 6.7%, respectively, at 7 years of age. At age 8, 48.3% of African-American girls and 14.7% of white girls had begun development."
What Factors Influence Early Puberty?
Early puberty, referred to as "precocious puberty" is not caused by any one factor. The neurological and hormonal systems that control the onset of puberty are complex, but research has determined a number of environmental and lifestyle factors that may be contributing to the decline in age.
Doctor McDougall credits the decrease in age of maturity in both girls and boys to "the gradual shift from a plant-based diet to a diet of animal-based, high-fat, highly-processed foods society." He goes on to say, "Diets high in meats, dairy products, and processed plant foods have been associated with earlier menarche while consuming a vegetarian diet and vigorous exercise delays the onset of menarche. Earlier and greater rises in hormone activity bring on earlier puberty." Click here to watch Dr. McDougall's 2-minute video on precocious puberty and here to view the longer (more detailed) version.
Excess Fat Produces More Estrogen
Rising rates of overweight and obesity contribute to early sexual development. Many studies confirm the association between children who are overweight and early puberty in girls. "Male hormones called androstenedione made in the adrenal gland and ovaries are converted in the fat cells into estrogen" Dr. McDougall states. Fat cells are like estrogen-producing factories. As the weight goes up, so do the hormone levels. "Excess body fat" Dr. Fuhrman adds, "alters the levels of the hormones insulin, leptin, and estrogen, and these factors are believed to be responsible for the acceleration of pubertal timing by obesity. Also, physical inactivity may decrease melatonin levels, which can also affect signals in the brain that trigger pubertal development." Because the high fat and calories from refined vegetable oils are quickly absorbed and stored as fat (within minutes after consumption) they too promote weight gain, thereby influencing earlier maturity. Soft drink consumption is another factor believed to accelerate early puberty.
Animal Protein Raises Hormone Levels
Animal protein is associated with the onset of early puberty while plant protein has the opposite effect. "The type of protein children eat, particularly the critical window of preschool age at 5-6 years old" Dr. Michael Greger writes, "appears to determine when they start puberty. Kids eating lots of animal protein at that age (meat, eggs, and dairy) prematurely start puberty an entire year earlier than those eating lots of plant protein. Children with higher intakes of vegetable proteins start puberty 7 months later than average, and children eating more animal protein start puberty 7 months earlier than average. Every gram of daily animal protein intake (the weight of a paperclip) is association with a 17% increase in the risk of girls starting their periods earlier than age 12. Meat increases the levels of the growth hormone IGF-1 which is associated with early onset puberty." These findings can also be seen in the American Journal of Epidemiology: "Menarche occurred earlier in girls who consumed more animal protein and less vegetable protein as early as ages 3–5 years. Menarcheal age was later in countries where dietary fiber intake was higher."
Doctor Fuhrman's research also confirms that animal protein in children age 3-7 has been associated with earlier menarche and that higher vegetable protein intake at age 5-6 is associated with later menarche. Additionally, "Meat and dairy consumption in children may also reflect ingestion of environmental endocrine-disrupting chemicals (EDCs) that have accumulated in animal tissues." (See below.)
The livestock industry uses anabolic steroids testosterone to increase muscle mass in their cattle which boosts the production of male sex hormones in both girls and boys. American beef was found to contain up to 600 more times the levels of estrogen than Japanese beef which may facilitate estrogen accumulation in the body. In fact, "The levels of anabolic steroids in meat can be so high that studies have shown that athletes who eat certain kinds of meat may be falsely accused of abusing steroids."
Sixty to Seventy Percent of Estrogen in our Food Comes From Dairy
The majority of retail milk comes from pregnant cows that are constantly impregnated to produce milk. Due to genetic and dietary manipulation, the dairy industry forces dairy cows to lactate throughout their entire pregnancies. Dr. McDougall reports that "Dairy foods account for about 60 to 70% of the estrogen that comes from food. The main source of this estrogen is the modern factory farming practice of continuously milking cows throughout pregnancy. As gestation progresses, the estrogen content of milk increases from 15 pg/ml to 1,000 pg/ml. Pregnancy causes high levels of estrogen to circulate in the animal's body and to become part of the cow’s milk, which the children drink. Studies funded by the dairy industry show a 10% increase in IGF-1 levels (powerful growth hormones) in adolescent girls from one pint daily. Hormones are also added to animal feeds to stimulate the animal’s growth." This is why commercial cow’s milk contains large amounts of estrogens and progesterone. The levels of sex steroid hormones in children more than triples within one hour of drinking cow's milk.
A study that Dr. Greger highlights states "The consumption of cow’s milk [in humans] interferes with the sensitive endocrine regulatory network from the fetal period into old age.” During puberty with the physiological onset of increased secretion of growth hormone, IGF-1 serum levels increase and are further enhanced by milk consumption.
Cow's milk contains both artificial and natural occurring hormones that increase hormone levels in humans. Approximately a dozen steroid hormones are detectible in milk. Buttermilk has the highest concentrations, followed by skim milk. Many customers purchase organic dairy products in an attempt to avoid added steroid hormones as well as the genetically modified growth hormone rBGH. Avoiding these added hormones is beneficial, however, organic milk can still contain up to 59 additional naturally occurring hormones. This can include 8 pituitary hormones, 7 hypothalamic hormones, 7 steroid hormones, 6 thyroid hormones, and 11 different growth factors.
High-Fat Foods = More Sex Hormones
The type of bacteria in the intestine can also increase estrogen levels. Dr. McDougall explains that a high-fat, low-fiber diet promotes the growth of certain bacteria that convert bile acids into sex hormones. The intestinal wall then absorbs these hormones and deposits them into the bloodstream. The liver produces bile acids to digest fats. A diet higher in fat produces more bile acids that are converted to sex hormones.
A high-fat diet also raises estrogen levels by recirculation estrogen back into the bloodstream. After estrogen has circulated throughout the body, the liver removes it and disposes of it into the intestine. So that the hormone won't be reabsorbed by the intestine, the liver produces a substance which attaches to the hormone that prevents it from being re-absorbed. Again, a diet high in fat and meats promotes the growth of bacteria that secretes an enzyme which breaks apart the non-absorbable substance which releases the hormones. These hormones are then reabsorbed back into the blood stream, resulting in higher estrogen levels. Click here to watch Dr. Neal Barnard's video on how a diet rich in plant foods removes excess estrogen from recirculating back into the bloodstream.
Endocrine-Disrupting Chemicals Elevate Hormones
Endocrine-disrupting chemicals (EDC) are ubiquitous in our environment and the rate that they break down is very slow. Although they pose a threat to adults, children's sensitive bodies are affected at a greater level. Doctor Michael Greger's video cites evidence linking sexual maturation with exposure to environmental pollutants and "those with the most circulating in their bloodstream are 10 times more likely to start their period early."
Dr. Fuhrman says that these hormonally active synthetic chemicals mimic, inhibit, or alter the action of natural hormones. The chemicals that we are exposed to on a daily bases are approved and enter the environment before they are tested for their endocrine disruption potential.
BPA is one of the most highly produced chemical in the world. Animal tests show that its properties mimic estrogen. It can be found in polycarbonate plastics, rigid cups, water bottles, food storage containers, the lining of canned food products and dental sealants. "BPA can leach from containers into food and beverages, especially during heating and washing. BPA exposure is associated with early puberty in girls." For more information on BPA click here.
Phthalates are another chemical of concern that Dr. Fuhrman says is associated with early breast development in girls. They can be found in toys, food packaging, hoses, raincoats, shower curtains, vinyl flooring, wall coverings, lubricants, adhesives, detergents, nail polish, hair spray, and shampoo. Click here for information on phthalates.
Endocrine-Disruping Chemicals Concentrate in the Fat of Animals
The concentration of EDCs increases significantly the higher up the food chain; eating lower on the food chain (plant foods) decreases our exposure to these toxins. The foods with the highest levels of chemical contamination are meat, poultry, fish, and dairy products. Dr. McDougall says that "The reason that these animal foods are the primary source of pollution is because their fatty tissues attract and concentrate chemicals - a process known as bioaccumulation." Although many countries have banned and restricted the use of many EDCs, the United States has been hesitant. According to Dr. Greger, "A half million tons of these chemicals continue to be spewed out into the environment every year, so much so that now, they come down in the rain, contaminate the soil and plants, but then concentrate up the food chain in the fat of animals. Animal products are thought to represent the most important source of human exposure to many organic pollutants. Water animals and birds concentrate these compounds to levels several thousands of times greater than those in the environment, because these are fat-soluble chemicals. Of then of course, we recycle the leftover remains of farm animals into farm animal feed, and so the levels can get higher and higher in animal food products."
Doctor Fuhrman emphasizes that exposure to EDCs during childhood is associated with hormonal cancers, such as breast and testicular cancers.
Doctor McDougall concurs, "The intake of high-fat foods--especially fish, meat, eggs, fats and oils, and dairy products--is the primary source of environmental chemicals in the American population. These chemicals are attracted to, and concentrated in fat--the fat in our foods and the fat in our bodies. Many of these chemicals (mostly pesticides), have an estrogenic effect. When studied singly these chemicals may have only a weak estrogenic effect. However, when the chemicals were tested in combination estrogenic activity shot up 160 to 1600 fold."
A study involving Korean children found that processed meat, fish and other seafood contained the highest levels of endocrine-disrupting industrial chemicals like the dioxins and PCBS.
Other EDCs such as the flame retardant chemical Alkylphenol, have also been found in high concentrations in chicken, fish (anchovies, mackerel, salmon and cod), fish oil capsules, pork, beef, turkey, lard, tallow, cow's milk, eggs, pet food, infant formula and human breast milk. The highest levels were found in breast milk of women who eat fish (due to bioaccumulation up the food chain).
Although banned in many other countries, Polychlorinated Naphthalenes (PCNs) can be found in farmed salmon, organic salmon, poultry, eggs, beef and lamb. Whole plant foods contain ten times less, and a hundred times less than fish.
Ways parents can help their children avoid toxins in their food
Dr. Fuhrman's article Girls are Reaching Puberty Earlier Than Ever offers several ways to avoid toxins:
- Children’s diets should focus on whole plant foods rather than animal foods – this will keep protein intake in a safe range and reduce their consumption of EDCs
- Minimize dairy products in children’s diets – use almond and hemp milks instead of cows’ milk
- Encourage children to exercise and exercise with them.
- Minimize processed foods – these are calorie-dense and nutrient-poor, and they promote obesity and other diseases.
- Children’s diets should include as wide a variety of natural plant foods as possible including, green vegetables, squashes, corn, carrots, tomatoes, onions, mushrooms, nuts, seeds, avocados, beans, fruits and whole grains. This means that healthy eating is a lifetime event.
- Buy organic produce when possible to avoid synthetic pesticides.
Ways to minimize exposure to BPA
- Avoid use of rigid polycarbonate plastics (recycling label #7) whenever possible.
- Do not use plastic water bottles.
- Do not microwave in plastic containers.
- Minimize the use of canned foods and avoid canned infant formulas.
Ways to Minimize Exposure to Phthalates
- Avoid plastics marked with recycling label #3 (PVC) whenever possible.
- Check ingredient lists on personal care products for phthalates. Also be aware that “fragrance” listed as an ingredient often means that the products contains phthalates. For more information, visit the Environmental Working Group’s guide to children’s personal care products.
Consequences of Early Puberty
Emotional and Social
Dr. McDougall points out that the onset of sexual maturity has many profound social, physical and emotional consequences on not only the child, but the family and society as well. "Precocious puberty" McDougall says, "causes children to have sexual desires and functions long before they are psychologically ready." Consequences of sexual activity among teens results in teenage pregnancies, single motherhood, divorce, discontinuation of the mother's education and poverty. Children are also at risk of contracting sexually transmitted diseases that can result in herpes, infertility and AIDS and difficult pregnancies. "A teenage mother is at greater risk of pregnancy complications, such as premature and prolonged labor, and preeclampsia, than older mothers. The baby is also at greater risk, with 9% low-birth weight deliveries. Low-birth weight babies have a higher risk of complications, like respiratory distress syndrome and bleeding, and they are at a 40-times greater risk of death during their first month of life compared to a normal weight infant."
Dr. Fuhrman adds, "Seven, eight and nine year old girls are not emotionally or psychologically equipped to handle puberty. Earlier puberty is also associated with a higher risk of psychological problems during adolescence such as anxiety, depression, and eating disorders. Girls who mature earlier are also more likely to take part in risky behaviors like smoking and alcohol use."
Early puberty is a risk factor for several diseases such metabolic syndrome, cardiovascular disease, hormone sensitive cancers and a shorter lifespan. Due to an extended time of exposure to hormones, early onset of menstruation is a well-documented risk factor for developing breast cancer in adulthood. According to the American Journal of Epidemiology, "There is substantial evidence that earlier menarche increases a female’s lifetime risk of breast cancer, possibly because of longer exposure to estrogens, and recent reports suggest that more rapid adolescent physical growth and earlier completion of adolescent growth may also increase lifetime risk of breast cancer."
The first ten years of a child's life is when diet offers the most powerful protection against reducing the risk of breast cancer. In Dr. Fuhrman's book Disease Proof Your Child, he explains how "the occurrence of breast cancer is three times higher in women who started puberty before age twelve. Individuals who develop breast cancer have been found to have higher blood levels of these hormones than those who do not develop breast cancer."
Women with breast cancer who started their menstrual cycle at or before the age of 11 years also have a lower rate of surviving from their breast cancer. "The optimal age of onset of periods with respect to survival was age 15 years."
Girls who start their menstrual cycle at a later age reduce their risk of breast cancer - thus increasing their lifespan. By reducing or eliminating animal products and increasing whole plant foods can delay puberty by approximately 7-8 months, which Dr. Greger says "may translate into a 6% reduction in breast cancer risk and an up to 3% decrease in total mortality. And not just a problem in girls, boys eating more meat in childhood appear more likely to grow up with the kind of abdominal fat deposits that increase risk for heart disease."
"Children who reach sexual maturity later in life also eventually grow taller as adults. The reason for this is that sex hormones close the growth (epiphysial) plates of bones, halting further longitudinal growth."
Take Away Message
The typical American diet rich in meat, dairy, eggs, processed and fast foods interrupts the normal hormonal development in adolescents. However, many lifestyle factors can be modified in order to delay puberty such as changing to a diet of predominately of whole natural plant foods, maintaining a healthy weight and exercising, and avoiding endocrine disrupting chemicals as much as possible. Dr McDougall emphasizes, "Even if your children and grandchildren have already have started precocious puberty, this process can be halted with a change in diet and associated weight loss. (Exercise encourages weight loss and lower sex hormones too.)"
Additional guides for choosing products free from endocrine-disrupting chemicals:
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