Dr. Lassek's talk may be viewed here: http://www.youtube.com/watch?v=gJhT_ANNy4E Abstract: One puzzle is why human males have such a strong preference for women with hourglass figures and low weights that can compromise fertility. The second is why slender young women typically have about one third of their weight in body fat, more than bears starting to hibernate, and why human infants are also very fat. Finally, why do women typically gain another twenty pounds or more during their reproductive years? The answer may lie in the roles that fat plays in providing essential fatty acids needed for the growth of a very large brain and in regulating overall fetal growth.

1. WHY DO
WOMEN
NEED FAT?
Will Lassek

2. Look
here
first

3. Who is the
most attractive
imaginary woman?
eg. animated films,
video games,
comics, graphic novels

5. Jessica Rabbit
“most attractive
imaginary
woman”
650 undergrads
of Steve Gaulin
“sexiest cartoon
character”
Cadbury contest

6. What is her
most
unusual
attribute?

7. Jessica Rabbit
Waist/Hip
Ratio: 38%
Waist/Height
Ratio: 15%
(10 inches)

8. 38%
68%
74%
WAIST/HIP
Playmate
undergrad

9. 15%
10 in
36%
24 in
44%
28 in
WAIST/HEIGHT
Playmate
undergrad

10. WHERE DO
MEN LOOK
FIRST &
LONGEST?

11. Cornellisen, et al. 2009
Look
here
first
eye tracking:
WAIST is
where men look
first and most
when judging
attractiveness

12. Why should we care what men
find attractive?
Look
here
first

13. Men should admire qualities
that help women have
children that survive

14. HOW IS WOMEN’S
WAIST FAT
CONNECTED
TO HAVING
CHILDREN?

15. BMI
Waist & BMI (Body Mass Index)
32
small waist
30
28 requires low BMI
26
correlation = 0.93
24
22 Playmates
20
undergrads
18
16
14
20 22 24 26 28 30 32 34 36
Jessica’s BMI? Waist, inches

16. Jessica Rabbit
waist/height
15%
predicted
BMI:
10
(from waist,
hip, height)

17. Average weight of young US women by BMI
150
Pounds
140
130
BMI <20
<120 pounds
120
110
100
90
16
17
18
19
20
21
BMI
22
23
24
25

18. Men prefer women with low BMI’s
Martin Tovee, et al. 1999
attractiveness
scores

19. Cumulative BMI % age 18-20, 1971-75
(before the obesity epidemic)
50
Percent
40
30
half of young women
had BMI’s <20
20
10
0
14
15
16
17
BMI
18
19

20. HOW DOES
A MOTHER’S
SMALL WAIST
& LOW BMI
AFFECT HER
CHILDREN?

21. OVULATORY INFERTILITY & BMI:
116,671 nurses, Rich-Edwards 2002
21
BMI<21:
HARDER
TO
GET
PREGNANT

22. In foraging/subsistence populations
thinner women have fewer children
Papua
New
Guinea
Andes
Brush 93
Mueller 79
Hadza
Marlowe 04

23. Lower BMI, bad for infants
0
Low Birth
Weight
Preterm
1
2
<19
19-24
25+
Hospital
(infant)
Murakami 2005
3

24. Low BMI & fetal or infant death
England
BMI
17
23
the lower
the BMI,
the more
infant
deaths
Tennant, 2011

25. PUZZLE
WHY DO MEN PREFER WOMEN
WITH LOWER FERTILITY
& LESS HEALTHY INFANTS?
AND (OR)
WHY DO MOST YOUNG
WOMEN HAVE SMALL WAISTS
& LOW BMI’S?

26. WHAT HAPPENS TO
A FIRST-TIME
AMERICAN MOTHER
EVERY 86 SECONDS?

27. WH, 1932 (1847) Catherine

28. FTA, 1932 (1929)

29. Evolution of pelvis in humans
pelvis changed to allow
upright walking and running

30. Smallest pelvic outlet dimension:
interspinous diameter ~ 9 cm
a
Interspinous

31. Average biparietal diameter at term: 9.5 cm

32. human
chimpanzee
humans have
much less of
brain growth
before birth,
but head is
still too big

33. Almost half of babies from “normal”
vaginal deliveries have bleeding in brain
46%
Rooks, 2008

34. LARGER HEAD
LEADS TO BLOCKED LABOR
AND DEATH IN CHILDBIRTH
Spain, ~1100 AD

35. HOW COMMON WAS
DEATH IN CHILDBIRTH
BEFORE
C-SECTIONS?

36. WHICH
SEX
LIVES
LONGER?

37. Average age at death,
US 1999-2010
60 62 64 66 68 70 72 74 76
men
women

38. 60
Percent surviving to age 65,
US 1999-2010
65
70
men
women
75
80

39. 26
Average adult age at death:
30,000 BC to 1799 AD
28
30
32
34
36
men
women
~3000 skeletons examined by Larry Angel, 1984

40. Sweden, 1800-1899
Hogberg, 1985
1 in 14 mothers
died in childbirth

41. Maternal deaths in 2000, WHO
many mothers
Sierra Leone
still die in Afghanistan
childbirth Malawi
Sierra Leone 1/50
Angola
Niger
Tanzania
Rwanda
Mali
2.0%
1.9
1.8
1.7
1.6
1.5
1.4
1.2

42. First C-sections by birth
US, 1990
25
most risk of
blocked labor
with first birth
% C-sections
20
15
10
5
0
1
2
3
Birth
4
5
6

43. Every 86 seconds a first-time
American mother has a C-section

44. WHAT IS THE
BENEFIT OF A
SMALLER WAIST
& LOWER BMI
IN A FIRST-TIME
MOTHER?

45. Head size cm
Lower BMI, smaller newborn
34.8
st
head for 1 birth
34.6
34.4
34.2
34.0
33.8
33.6
33.4
10-14
15-19
20-24
25-29
30-34
BMI before pregnancy
35-39

46. Percent C-sections
Lower BMI, fewer C-sections
st
40
for 1 birth
35
30
25
20
15
10
5
0
less blocked babies
12 14 16 18 20 22 24 26 28
BMI before pregnancy

47. High blood pressure during
pregnancy can also be bad
preeclampsia/eclampsia

48. More high blood pressure with
first pregnancy
Percent
4
3
2
1
0
1
2
3
4
5
Pregnancy
6
7

49. Percent preeclampsia
BMI & high blood pressure
st
in 1 time mothers
24
22
20
18
16
14
12
10
8
6
4
lower BMI,
less risk
14
16
18
20
22
24
26
28
30

50. WHAT ARE THE
BENEFITS OF A
SMALLER WAIST
& LOWER BMI
IN A FIRST-TIME
MOTHER? (2)

51. 1. LESS RISK OF
MOTHER & CHILD
DYING IN
CHILDBIRTH
2. LESS HIGH
BLOOD PRESSURE

52. WHAT HAPPENS TO
WOMEN’S WAIST FAT
(AND WEIGHT)
AFTER
HAVING A CHILD?

53. Waist, inches
Minimum waist (inches) in women
33 with children, US 1988-94
32
31
30
29
28
27
26
25
NP
15 15 20 25 30 35 40 45 50
Age Group

54. Average weight in American women
150before
Weight, pounds
145
obesity epidemic
1959-61
140
135
130
125
120
as add 25-30 pounds,
more new fat in waist
18 22 26 30 34 38 42 46
Age

55. Average BMI in European women
20
Age 17-18
All Adults
21
BMI
22 23 24
122 pounds
150 pounds
25
26

56. WHY IS IT BENEFICIAL
TO HAVE MORE
WAIST FAT AFTER
HAVING A CHILD?

57. Bigger waist, bigger babies
0
Adjusted Odds Ratio
1
2
3
LBW
Preterm
<19
19-24
25+
Hospital
(infant)
Murakami 2005

58. Pelvic width, cm
Pelvic width and births, NHANES III
30.5
30.0
29.5
29.0
28.5
28.0
27.5
27.0
birth canal expands
with each birth, so
less blocked labor
0
1
2
3
4
Births
5
6

59. LESS HIGH BLOOD PRESSURE
2nd CHILD WITH SAME FATHER

60. Insulin
Bigger waist, more insulin resistance
120
110
100
90
80
70
60
50
40
30
more insulin resistance =
more sugar for baby
= bigger baby
38 40 42 44 46 48 50 52 54 56 58 60 62
Waist/Height x 100

61. Triglycerides
Bigger waist, more triglycerides
170
160
more fat in
150
mother’s blood =
140
130
bigger baby
120
110
100
90
80
70
36 38 40 42 44 46 48 50 52 54 56 58 60 62
Waist/height x 100

62. BMI in women 15+ in 190 countries
2/3rds are 25+
“overweight”
Percent
100
90
80
70
60
50
40
30
20
10
0
20 21 22 23 24 25 26 27 28 29 30 31+
Cumulative BMI in women 15+

63. WHERE WOMEN
DON’T ADD WAIST FAT,
CHILDREN SUFFER
(CONTROLLING FOR INCOME)

64. Low Birth Weight %
Low birth weight & average BMI
20 in women (income controlled)
15
10
5
<22
22
23
24
25
26
Female BMI
27
28
29+

65. Deaths per 1000 births
Newborn death rate & average BMI
in women (income controlled)
50
40
30
20
10
0
<23 23 24 25 26 27 28 29+
Female BMI

66. Child death rate & average BMI
in women (income controlled)
Deaths per 1000 births
125
100
75
50
25
<23 23
24
25 26 27
Female BMI
28
29+

67. SO, WHY
DOES A
WOMAN
NEED
WAIST FAT?

68. WAIST FAT
DETERMINES
THE SIZE OF
HER
CHILDREN

69. WHAT
ABOUT
FAT in the
HIPS
& LEGS?

70. Jessica Rabbit
HIP/HEIGHT
= 53%
(36 in)

71. 53%
53%
53%
Hip/height
BMI <20
Playmate
undergrad

72. Men’s ranking of desirability of
women’s body areas
Rank Score 1-5
Chest
1
4.13
Buttocks
2
4.09
Legs
3
4.04
Hips
4
3.98
Montoya, 2006

73. Almost all cultures value
fat in women’s legs & hips
Brown & Konner, 1987

74. What % of weight is fat?
Ambelosi baboon

75. What % of weight is fat?
bear ready to hibernate

76. What % of
weight is fat?
typical
undergrad

77. height: 64”
weight: 132 lb
BMI: 22.2
fat: 32%
(42 lb)

78. WHY DO WOMEN
NEED
SO MUCH FAT?

79. 2/3rds of fat is
in hips & legs
(white = fat)

80. LOWER BODY FAT
IS LOCKED AWAY
UNTIL LATE IN
PREGNANCY

81. Mothers eat less in late pregnancy
2600& while nursing (calories/day)
30%
of fetal
growth
2400
2200
2000
1800
0
1-6
7
8
9 nurse
Months of pregnancy
COST

82. AS EAT LESS,
LOWER BODY FAT
IS MOBILIZED IN
LATE PREGNANCY
& WHILE NURSING
~1 ounce/day

83. WHAT IS IN
ONE OUNCE OF
LOWER-BODY
FAT?

84. Maternal energy cost of nursing: cals/kg
Prentice 1988
rat/pig
rabbit
sheep
guinea pig
beef cow
2% FAT
baboon
human
300 calories/day
0
50
100
150
200
250

85. WHAT IMPORTANT
ORGAN IN
A NEW BABY
GROWS THE MOST
& ADDS
THE MOST FAT?

86. Brain triples in size in 1st year
Brain weight, g
900
800
700
600
500
400
300

87. Fat = 52% dry weight of brain
Fat
Protein

88. Nerve cells are mostly membranes
made of fat with embedded proteins

89. Nerve cell membranes would
cover 5 football fields

90. DHA = 1/3 of membrane fat
rd
DOCOSAHEXAENOIC ACID
DHA

91. DHA (docosahexaenoic acid)
omega-3
22 carbons
6 double bonds
omega-3 fats must come from diet

92. DHA is active in every part of nerve cell
makes
synapse work
grows
axon
transmits
signal
makes & grows dendrites
preserves
Calderon 07

93. Children of mothers with more DHA
while pregnant have higher verbal IQ’s
% higher IQ
85
80
75
70
65
60
low
medium
high
Mother's dietary DHA
Hibbeln, 07

94. More DHA in mother’s milk: higher
PISA math score in 28 countries
540
Math Score
520
500
480
460
440
420
1
2
3
Milk DHA index
4+

95. WHERE DOES
MILK DHA
COME FROM?

96. Where does milk DHA come from?
CURRENT
DIET
BODY FAT
80%
Fidler 2000

97. DHA mainly from stored fat
80% of 120 mg
MILK DHA
= 96 mg*
ONE OUNCE
OF FAT =
96 mg* DHA
*120 mg DHA/day
* European mothers

98. SO, WHY DO WOMEN
NEED SO MUCH
LOWER-BODY
FAT?

99. LOWER-BODY
FAT PROVIDES
ESSENTIAL FATS
NEEDED BY BRAIN

100. WHY ARE
OUR
NEWBORN
BABIES
SO FAT?

101. TYPICAL NEWBORN
HAS 2 POUNDS OF FAT
WITH
1500 MILLIGRAMS OF
DHA
(1.6%)

102. HOW CAN WOMEN
STORE MORE DHA WHEN
DHA % IN FAT IS LOW
BECAUSE OF
LOW DHA FROM DIET?

103. Percent DHA in body fat
Imaichi 65, Leaf 95
Japan
US
0.0
0.2
0.4
0.6
0.8
1.0
1.2

104. Female obesity %
DHA in mother’s milk &
female obesity in 43 countries
30
25
USA?
Japan?
paleolithic?
20
15
10
5
0
1
2
3
4
Milk DHA index
5
6+

106. BMI
Waist/Height & BMI (Body Mass Index)
32
small waist
30
28 requires low BMI
26
correlation = 0.93
24
22
undergrads
20 Playmates
18
16
30 32 34 36 38 40 42 44 46 48 50 52 54
Jessica?
Waist/Height x 100

107. 2%
1%

108. Low birth weight %
Lower BMI mothers have more
9
low birth weight babies
8
7
6
5
10 to 14
15 to 19
BMI
20 to 29