Dr. Natalie Luscombe-Marsh's seminar discusses the impact of dietary protein on weight loss, appetite regulation, and gastrointestinal function. High-protein diets are shown to enhance thermogenesis and suppress appetite, leading to better weight management compared to high-carbohydrate diets. Current research aims to explore how different protein loads affect appetite, gastrointestinal motility, and energy intake in both lean and obese individuals.

1. The Waite Research Institute
FOODplus Research Centre
Scientific Seminar Series – 2010
#3b
Dr Natalie Luscombe
Life Impact | The University of Adelaide

2. Dietary protein, gastrointestinal
function and the regulation of
energy intake and body weight
Dr Natalie Luscombe-Marsh
FOODPlus Seminar, August 19th 2010
University of Adelaide Discipline of Medicine, NHMRC Centre of
Clinical Research Excellence in Nutritional Physiology, Australia
Centre of
Clinical
Research
Excellence
Nutritional Physiology,
Interventions & Outcomes

3. Overview
• The effects of high-protein diets on weight loss and the
relationship between protein-induced thermogenesis and
weight loss
• Background that suggests that the suppression of
appetite and energy intake is a more important
mechanism underlying the regulation of body weight
• The role of gastrointestinal mechanisms in modulating
appetite and energy intake in response to fat and
carbohydrate
• Current research being undertake to examine the role of
gastrointestinal mechanisms in regulation appetitive-
responses to dietary protein

4. Introduction
• Diet is an important factor in the prevention and
management of obesity
• Increasing evidence suggests replacing some
carbohydrate in the diet with either unsaturated-fat or
protein, facilitates weight loss and maintenance
•[Paddon-Jones et al., 2008; Shai et al., 2008; Weigle et al., 2005]

5. Diets higher in protein or unsaturated fat
improve weight loss & maintenance
Skov et al. 1999 3.8 kg > wt loss with HP vs. SP
Foster et al. 2003 3.8 kg > wt loss with HP vs. SP at 6 mth
1.8 kg > at 12 mth
Brehm et al. 2003 4.6 kg > wt loss with HP vs. SP
Samaha et al. 2003 3.9 kg > wt loss with HP vs. SP
Yancy et al. 2004 5.5 kg > wt loss with HP vs. SP
Lejeune et al. 2005 2.5 kg > wt loss with HP vs. SP at 6 mth
Brinkworth et al. 2004 1.5 kg > wt loss with HP vs. SP at 12 mth
Brinkworth et al. 2004 1.2 kg > wt loss with HP vs. SP at 12 mth
Keogh et al. 2007 2.8 kg > wt loss with HF vs. HP at 12 mth

6. Mechanisms underlying protein-induced
weight loss and maintenance
• Increased thermogenesis
• Suppression of appetite and energy intake

7. Differential effects of meals high in protein
carbohydrate or fat on thermogenesis
25
HP SP
Isocaloric meals 2.4 – 2.9 MJ
% Energy protein:carbohdrate (P:C)
20 TEF measured over a period of 2 - 24 hrs
S
15
TEF
DIT S
(% of EI)
S SN
10
S
S
5
P: C P: C P: C P: C P: C P: C P: C P: C P: C P: C P: C P: C
46/46 12/69 32/54 10/77 37/32 18/32 46/46 12/69 29/61 9/30 14/59 5/64
0
Luscombe et al. Luscombe et al. Luscombe-Marsh Luscombe-Marsh Westerterp- Schutz et al.
2002 2003 et al. 2005 et al. unpublished Plantenga et al. 1987
(T2DM) (Hyperinsulinemic) (Hyperinsulinemic) (Healthy men) 1999 (Healthy) (Elderly men)

8. Thermogenic effect of a high-protein diets is
maintained over 12-16 wks
10
HP SP SN
9 Isocaloric meals 2.4 – 2.9 MJ
% Energy P:C
8 TEF measured over a period
of 2 - 3 hrs S
7
S
6
TEF 5
(% EI)
4
3
2
P: C P: C P: C P: C P: C P: C
1
46/46 12/69 32/54 10/77 37/32 18/32
0
Luscombe et al. 2002 Luscombe et al. 2003 Luscombe-Marsh et al. 2005
(T2DM) (Hyperinsulinemic) (Hyperinsulinemic)

9. Implications of protein-induced TEF
for the regulation of body weight
• If we assume, a high-protein diet causes a 2% point
greater TEF and individuals on average consumed 7500
kJ/d, then this equates to wasting ~150 kJ/d or 54,750
kJ/yr.
• theoretically, this may cause a greater weight loss
(by ~1.4 kg) on a high-protein compared to high-
carbohydrate diet, over 1 year
• The av. Australian gains ~ 0.5 kg/yr which equates to an
excess of ~56 kJ/d or 20,350 kJ/yr
• theoretically, a high-protein diet may prevent this
gradual increase in weight

10. Mechanisms underlying protein-induced
weight loss and maintenance
• Increased in postprandial thermogenesis
• Suppression of appetite and subsequent reduction in
energy intake

11. Effect of a high-protein ad libitum diet
on appetite, energy intake and weight loss
Weigle et al. Am J Clin Nutr 2005;82:41-48

12. Differential acute effects of macronutrients
on appetite and energy intake
Animal studies
• protein > carb > fat
[Geliebter, 1979; Walls and Koopmans, 1992]
Human oral studies
• protein > carb and/or > fat
[Batterham et al., 2006; Poppitt et al., 1998; Rolls et al., 1994; Rolls et al.,1988]
• fat ≡ carb and/or ≡ protein
[Vozzo et al., 2002; Rolls et al., 1991]

13. Gastrointestinal mechanisms that modulate
appetite and energy intake
Small intestinal
fat or glucose Slow
Gastric
Δ Gastric volume Emptying
&
Δ Motility Suppress
Energy Intake
Δ Hormones
Houghton et al. 1988, Chapman et al. 1999

14. Effects of macronutrients on gastric volumes
Fat or glucose  proximal gastric
relaxation
↑ antral filling and
distension
Sturm et al, 2004

15. 2200
n=12
1800 R = - 0.584
P < 0.001
Energy 1400
intake
(kcal) 1000
600
200
1 2 3 4 5 6 7 8 9 10 11
Antral area (cm2)
(Sturm et al. 2004)

16. Effects of nutrients on small intestinal
motor function
Small intestinal
fat or glucose
Motility
antral
pressures
isolated
pyloric pressures
(IPPWs)
duodenal
pressures
Heddle et al. 1988

17. Relationship between isolated pyloric pressures
and energy intake
N = 10 healthy subjects undergoing an i.v. infusion of CCK-8
8 r = - 0.7
P = 0.02
7
6
(MJ)
5
4
3
2
0 20 40 60 80 100 120 140
Total No. IPPWs
Brennan et al, 2007

18. Effects of nutrients on intragastric and
small intestinal hormonal release
nutrients
Hormones
ghrelin
CCK
PYY &
GLP-1
Lieverse et al. 1994, Feinle-Bisset et al. 2005

19. Changes in gastrointestinal function and the
suppression of energy intake are dependent on the
dose of nutrient administered
IL 0.25
IL1.5
IL 4 kcal/min
◊ saline (control)
kcal/min
Pilichiewicz et al. 2007

20. Changes in gastrointestinal function and the
suppression of energy intake are dependent
on the degree of nutrient digestion
• Delayed gastric emptying, particularly from the
proximal stomach
• Increased CCK and PYY release
• Suppression of hunger
• A 132 kcal ↓ in energy intake
Little et al. 2007

21. Aims of current research
1) To characterise the effects of :
• Protein load
• The degree of hydrolysis of protein
administered small-intestinally on antropyloroduodenal
(APD) motility and GI hormone release
2) To characterise the effects of protein load administered
orally on gastric emptying, meal distribution, orosensory
factors and GI hormone release
3) To determine whether the observed effects of protein
under these conditions are related to subsequent effects
on appetite and energy intake
in healthy lean and obese males

22. STUDY: 1
Effects of intraduodenal protein load on APD
motility, gastrointestinal hormone secretion,
appetite, and food intake in lean and obese males

23. Hypothesis
The acute suppression of appetite and energy intake by
small intestinal protein is:
1) load-dependent
2) related to changes in APD motility and GI
hormone secretion
in lean and obese men

24. Subjects
• 32 male subjects
16 lean
- BMI 18 - 25 kg/m2
16 obese
- BMI 30 - 35 kg/m2
• aged 18 - 55 years old

25. Study design
4 study days
60 minute infusion of:
1) saline control
whey protein hydrolysate:
2) 0.5 kcal/min
3) 1.5 kcal/min
4) 3 kcal/min
delivered at 4mL/minute

26. Study protocol
Antropyloroduodenal motility
Duodenal infusion
Buffet
meal
-10 0 15 30 45 60 90 Time (min)
Blood sample
Visual analogue scale
I feel hungry
Not at all Very much

27. Intraduodenal catheter
Pylorus
TMPD
(0 mV)
Antrum
TMPD
Duodenum (-40 mV)
Infusion port

28. Antropyloroduodenal pressure patterns
Antrum
Pylorus 40 mmHg
Duodenum

29. Study protocol
Antropyloroduodenal motility
Duodenal infusion
Buffet
meal
-10 0 15 30 45 60 90 Time (min)
Blood sample
Visual analogue scale

30. Effects of protein load on energy intake
1800
n=7
1600
1400
1200
(kcal)
1000
800
600
400
200
0
0 kcal/min 0.5 kcal/min 1.5 kcal/min 3 kcal/min

31. Effect of protein load on hunger
10
0
0 15 30 45 60 90
0 kcal/min
-10
VAS score (mm)
0.5 kcal/min
-20 1.5 kcal/min
3 kcal/min
-30
-40
-50

32. Effect of protein load on total number of
IPPWs
120 n=7
100
80
0 kcal/min
0.5 kcal/min
60 1.5 kcal/min
3 kcal/min
40
20
0

33. Translation of findings
• May aid in optimising current dietary strategies used in
the treatment of obesity.
• May identify and improve protein ingredients that can be
incorporated into functional foods that target satiety and
energy intake.

34. Questions
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Clinical
Research
Excellence
Nutritional Physiology,
Interventions & Outcomes