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Weight and Fertility

Weight is a core issue for our sex hormones and fertility, and a classic example of this is a girl’s menarche (her first period) has been stable to the weight of about 104.5lbs (47.5 +/- 0.5 Kg) over the last 120 years.  However, girls now reach that weight (and the menarche) at about 12½, while it was 16½ in 1900. This dramatic four-year age change is purely down to a girl’s weight altering her hormone balance, and the weight-hormone relationship will continue throughout her life.

The health of our weight is usually the “Body Mass Index” (BMI), which is a simple calculation between height and weight, and the ranges are:

  • Under 18.5 is underweight
  • 18.6 to 24.9 is normal
  • Above 25 is overweight
  • Over 30 is obese

In general, being a healthy weight coincides with good fertility, and fertility falls the further away we get from a normal BMI. The worst problem for fertility is that faced by underweight women, as they’re vulnerable to low hormone levels that disrupt or stop cycles. However, the most common weight-related fertility problem is excess weight, especially in the West:

  • 35.7% of USA adults were obese in 2010 i
  • Nearly a third (32%) of 20-39-year-old USA women were obese in 2011
  • 86.3% of USA adults are expected to be overweight in 2030
  • 51.1% of USA adults are expected to be obese in 2030

By 2030 it’s expected that 16-18% of the total US healthcare costs will be on obesity-related illnesses. ii

High BMI and health

Having a high BMI increases the risk of a range of health issues, including:

  • Infertility
  • Cardiovascular disease
  • Hypertension
  • Diabetes

The average weight has been rising since a rapid rise in childhood obesity rates in the 1970s because iii

  • More “empty calories” consumption in high-calorie foods and drinks rather than “proper meals”
  • More food is eaten away from home or in convenience foods
  • Children are burning fewer calories in activities like walking to school
  • Kids spend more time watching television, using computers, and surfing the web

Female fertility and weight

Having an average weight maximises a woman’s fertility, and while obesity reduces a woman’s fertility, it’s not as bad as being too thin:

  • Women with a BMI below 17 are 1.6x more likely to be infertile
  • Underweight women are 1.3x more likely to have pre-term births
  • Obese women take longer to get pregnant than normal BMI women iv
  • Miscarriage rates are higher for obese women v
  • Fertility treatment costs are 54% higher for “overweight non-ovulating” women than “normal weight non-ovulating women”
  • Fertility treatment costs for “obese non-ovulating women” are 100% higher than “normal weight non-ovulating women” vi

Male fertility and weight

The rise in male infertility over the past 30 years has coincided with a three-fold increase in obesity in men of reproductive age. There’s evidence that obesity changes structures in the testes, lowers sperm quality and reduces a man’s potential to have children: vii

  • An increase in BMI by as little as three units lowers male fertility viii
  • Obese men are 3x more likely to have low semen quality than average-weight men ix
  • Rises in BMI reduce sperm concentration and motility x
  • Overweight men have more damage to their sperm DNA xi
  • Obesity causes erectile dysfunction because a hormone (aromatase) in fat tissue converts testosterone to estrogen
  • Male obesity affects the metabolic and reproductive health of their children, with evidence that paternal health cues pass to the next generation xii

There are some simple ways to assess and improve male fertility.

Childhood outcomes

Weight issues tend to run in families, and overweight parents increase the chances that their adult children will have:

  • Type II diabetes xiii
  • Obesity
  • High cholesterol
  • Hypertension xiv
  • Stroke
  • Heart attack xv
  • Asthma
  • Autism

Changing weight

Somewhat surprisingly, both under- and over-weight people face similar issues:

  1. Their digestion is failing to nourish and support the body, which can cause body fluids to accumulate
  2. Their microbiome is unbalanced and weakens digestive function, and it’s known faecal transplants of healthy microbiomes successfully treat both underweight and overweight conditions xvixvii
  3. Poor diet choices fundamentally affect microbiome health
  4. Unhealthy emotional relationships with food are complex and difficult to manage

Long-lasting weight change is impossible without lifestyle changes, or any weight lost or gained will revert to “what was normal” quickly as any weight change needs to be maintained for a year to become the “new norm”. Achieving a healthy weight has to focus on strengthening digestion in a gradual and sustained way.

Crash dieting

  • Denies people their nourishment and leaves them feeling denied
  • Weakens digestion
  • It makes the situation worse in the long term and reduces fertility

Exercise helps promote digestive function by burning calories and improving fluid and hormone balance, but it needs to match Personal Fertility Profiles (PFPs). For many people losing (or gaining) weight is a vital way to raise their fertility, and when overweight or obese women:

  • Lose 10% of their body weight their body fat falls by 30%
  • Most obese women resume ovulating after a 10% weight loss
  • Losing 10.2kg (22lb) results in 90% of obese women resuming ovulation xviii

There are simple rules on how to lose weight:

  • It’s easier to succeed if you’re part of a group, so get some support!
  • A routine is essential; put a structure in place to support yourself and avoid questioning what you should be doing all the time. You’ve made a choice; now, just follow it through
  • Missing meals weakens digestion, and your diet should strengthen your digestion, not weaken it (see Energy)
  • Avoid sugar (think of it as poison) as it gives people a quick “burst” and a very long “down”
  • Try to avoid thinking you’re being denied food/sugar and focus on positive outcomes because no one will put up with their treats being taken away, so change the emotional language around food
  • Changing food types and portion sizes alter energy levels and the palette in a surprisingly short time. Listen to your body and how it reacts to food, definitely eat more whole foods and vegetables and try cooking a bit more
  • Reinforcing achievements is essential and heartening: be proud of what you can do, not focus on what you “should have done”

iPrevalence of obesity in the United States, 2009–2010’. Ogden CL, et al. NCHS Data Brief 2012, 82:1–8.
iiWill all Americans become overweight or obese? Estimating the progression and cost of the US obesity epidemic.’Wang Y et al. Obesity (Silver Spring). 2008 Oct;16(10):2323-30.
iiiChildhood obesity: trends and potential causes.’ Anderson PM1, Butcher KE. Future Child. 2006 Spring;16(1):19-45.
ivThe influence of maternal and paternal factors on time to pregnancy–a dutch population-based birth-cohort study: the GECKO drenthe study.’ Mutsaerts MA, et al. Hum Reprod 2012, 27:583–593.
vDoes obesity increase the risk of miscarriage in spontaneous conception: A systematic review.’ Boots C, Stephenson MD. Semin Reprod Med 2011, 29:507–513.
vi‘Economic consequences of overweight and obesity in infertility: a framework for evaluating the costs and outcomes of fertility care.’Koning AM et al. Hum Reprod Update. 2010 May-Jun;16(3):246-54.
viiImpact of obesity on male fertility, sperm function and molecular composition’ Nicole O. Palmer,et al. Spermatogenesis 2:4, 1-11; October/November/December 2012
viiiReduced fertility among overweight and obese men’. Sallmen M, et al. Epidemiology 2006, 17:520–523.
ixPersistent organochlorines, sedentary occupation, obesity and human male subfertility.’ Magnusdottir EV, et al. Hum Reprod 2005, 20:208–215.
xOverweight and seminal quality: a study of 794 patients.’ Martini AC, et al. Fertil Steril 2010, 94:1739–1743.
x‘Body mass index in relation to semen quality, sperm DNA integrity, and serum reproductive hormone levels among men attending an infertility clinic.’ Chavarro JE, et al. Fertil Steril 2010, 93:2222–22231.
xii‘Impact of obesity on male fertility, sperm function and molecular composition’ Nicole O. Palmer,et al. Spermatogenesis 2:4, 1-11; October/November/December 2012
xiiiFetal nutrition and adult disease KM Godfrey, DJP Barker – The American journal of clinical nutrition, 2000
xivDiet in pregnancy and the offspring’s blood pressure 40 years later DM Campbell, MH Hall, DJP Barker, J Cross, et al. BJOG: An International Journal of Obstetrics & Gynaecology1996/3/1
xvFetal nutrition and cardiovascular disease in adult life DJP Barker, KM Godfrey, PD Gluckman, JE Harding et al. The Lancet, 1993/4/10
xvi<“Gut Microbiota from Twins Discordant for Obesity Modulate Metabolism in Mice” Vanessa K. Ridaura Et al. Science06 Sep 2013
xvii<“Weight Gain After Fecal Microbiota Transplantation” Neha Alang, Colleen R. Kelly; Weight Gain After Fecal Microbiota Transplantation, Open Forum Infectious Diseases, Volume 2, Issue 1, 1 January 2015, ofv004,
xviiiWeight loss in obese infertile women results in improvement in reproductive outcome for all forms of fertility treatment.’ Clark AM, et al. Hum Reprod 1998, 13:1502–1505.