Meal size, high fat versus sugar and meal size

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Hi All,

High fat diets have been associated with weight gain, but what about the size of

the

meals that are eaten and other cues possibly affecting the results? Is it

possible

that, although diets contained " evaporated milk, sucrose, corn oil and

micronutrients " , other macronutrient sources may have affected the result?

See the pdf-available below paper.

Synowski SJ, Smart AB, Warwick ZS.

Meal size of high-fat food is reliably greater than high-carbohydrate food

across

externally-evoked single-meal tests and long-term spontaneous feeding in rat.

Appetite. 2005 Oct;45(2):191-4.

PMID: 15922489

Abstract

A series of studies in rat using isoenergetic (kcal/ml) liquid diets differing

in

fat content has previously found dietary fat to dose-dependently increase daily

caloric intake. In single-meal tests in which meal initiation was externally

evoked

in feeding-associated environments, the behavioral expression of this overeating

was

found to be larger meal intake. The present studies confirmed the ecological

validity of this larger meal size of high-fat diet (HF) relative to

high-carbohydrate diet (HC): meal size of HF>HC in home-cage testing (Experiment

1),

and during undisturbed, spontaneous feeding in which ingestive behavior was

continuously monitored (Experiments 2 and 3). These findings demonstrate that

single-meal paradigms yield results consistent with spontaneous feeding of

high-fat

and high-carbohydrate liquid diets ... elevated caloric intake associated with

chronic consumption of a high-fat diet.

.... In humans ... numerous confounds of dietary fat content with other dietary

and

lifestyle factors prevents inference of causality. Experimental research in

humans

has yielded mixed results: an intake-stimulatory effect of increased dietary fat

has

been noted by some but not all investigators, probably due to methodological

variations and the confounding of fat content with palatability and/or caloric

density (reviewed in Rolls and Hammer, 1995 and Warwick, 1996). ...

.... high-fat diet hyperphagia, isoenergetic (both 2.3 kcal/ml; 9.62 MJ/ml)

liquid

diets differing in fat:carbohydrate ratio were developed (Warwick & Weingarten,

1995). Reliably, the high-fat (HF) diet elicited greater daily energy intake and

weight gain than the high-carbohydrate (HC) diet across a variety of paradigms,

including oral feeding both with ad lib chow (Warwick et al., 2002 and Warwick,

2003) and without chow (Warwick & Weingarten, 1995); self-regulated intragastric

feeding both with chow (Lucas et al., 1998 and Warwick et al., 2003) and without

chow (Warwick and Weingarten, 1995 and Warwick et al., 2003); when diets were

gelled

to semi-solid form, and when energy density was halved by addition of water

(Warwick

et al., 2002). A linear dose–response relationship between dietary fat content

(ranging from 17 to 60% of energy) and daily energy intake has also been

demonstrated (Warwick, 2003).

Behaviorally, the greater daily energy intake associated with HF must reflect

larger

and/or more frequent meals relative to HC. To investigate the behavioral

expression

of high-fat diet hyperphagia, HF and HC were compared in single-meal tests and

in

preloading paradigms. Reliably, meal size (energy) of HF exceeded that of HC

(Warwick et al., 2000 and Warwick and Synowski, 1999), indicating that

meal-terminating mechanisms are less potently engaged by fat than by

carbohydrate.

In addition, preloading studies have demonstrated that HF elicits less

postprandial

satiety per kcal than HC (Warwick et al., 2000 and Warwick, 2003).

.... Experiment 1: meal size in home cage

.... Twelve male Long- rats ... diets were prepared from evaporated milk,

sucrose, corn oil and micronutrients, contained equivalent protein (7% of

energy),

and were isocaloric at 2.3 kcal/ml (9.62 MJ/ml). The HF diet provided 60% energy

from fat and 33% energy from carbohydrate, while in the HC diet the proportions

were

16% energy from fat, 77% from carbohydrate. ...

Intake of HF (mean 37.4 s.e. 1.9 kcal; 156.5 s.e. 7.7 MJ) was greater than

intake of

HC (mean 24.4 s.e. 2.0 kcal; 102.1 s.e. 8.4 MJ), t(11)=4.97, p<0.001.

.... sixteen additional rats were first trained to initiate feeding in response

to a

buzzer-light conditioned stimulus (CS) ... under two conditions: (1) in the

chambers

following presentation of the CS, and (2) in the home cage, with conditions

alternated until intake stabilized. ... no significant effect of test condition,

F(1,15)=0.05, n.s., but the expected significant effect of diet, F(1,15)=23.8,

p<0.001, with meal size of HF (mean 32.6 s.e 2.3 kcal; 136.4 s.e. 9.5 MJ) again

larger than HC (mean 23.2 s.e. 2.1 kcal; 97.1 s.e. 8.7 MJ).

.... Experiment 2: meal size during spontaneous feeding

.... neophobia ... Twenty-three new rats ... allowed to acclimate to either HF or

HC

ad lib for 8 days ... ad lib intake continued for an additional 8 days ... a

meal

defined as a period of licking behavior composed of at least 10 licks with

interlick

intervals (ILIs) no longer than 10 min. ...

Daily intake by rats fed HF was greater than rats fed HC, t(21)=3.24, p<0.05...

attributable to larger meals of HF relative to HC (t(21)=2.60, p<0.05; meal

frequency did not differ between HF and HC, t(21)=0.42, n.s. (Table 1).

Table 1. Daily intake and meal sizes on high-fat diet (HF) and high-carbohydrate

diet (HC)

=====================================

Experiment----2 Experiment 3

HF HC----Acclimation HF HC

N 12 11 11 5 6

Mean (SEM) Mean (SEM) Mean (SEM) Mean (SEM) Mean (SEM)

=====================================

Energy/day

kcal 158.1 (8.9) 118.4 (8.3) 110.0 (5.9) 119.1 (9.7) 92.0 (7.0)

MJ 661.5 (37.4) 495.4 (34.6) 460.2 (24.8) 498.3 (40.6) 384.9 (29.6)

Meal size

kcal 17.9 (1.7) 12.4 (1.2) 8.17 (1.5) 13.5 (1.6) 6.5 (0.5)

MJ 74.9 (7.3) 51.9 (4.8) 34.2 (6.3) 56.5 (6.7) 27.2 (2.1)

Number of meals per day

10.2 (0.8) 10.8 (1.2) 15.3 (2.2) 9.4 (0.8) 15.7 (1.7)

.... Experiment 3: spontaneous feeding following acclimation to mid-fat diet

.... To reduce the novelty of the HF and HC diets while still permitting the

formation of weight-matched diet groups ...

For 14 days, 11 new rats consumed a 1:1 (vol:vol) mixture of HF and HC, which

provided 38.5% energy from fat and 54.5% energy from carbohydrate. Following

this

acclimation period, two weight-matched groups were formed and fed either HF

(n=5) or

HC (n=6) for an additional 8 days. ... rats fed HF consumed more energy than

rats

fed HC, t(9)=2.31, p<0.05. Rats on HF increased their energy intake relative to

the

acclimation phase, while rats on HC decreased energy intake (Table 1). ...

Meal size of HF was larger than HC, t(9)=4.57, p<0.05, consistent with findings

in

Experiments 1 and 2. Rats on HF substantially increased meal size relative to

the

acclimation phase, while rats on HC showed a modest decrease. Meal frequency of

HF

was less than HC, t(9)=3.18, p<0.05. Rats on HF consumed fewer meals relative to

the

acclimation phase, while the number of meals eaten by rats on HC did not change

(Table 1).

General discussion

... results of the present study agree with observations from another model of

spontaneous feeding, self-regulated intragastric infusion. In this paradigm,

rats

spontaneously infused larger meals of HF relative to HC even though the taste

associated with both diets (sweet solution) was identical (Warwick et al, 2003).

The

number of daily meals was similar for both diet groups, producing greater total

energy intake for rats on HF. This finding indicates that macronutrient-specific

effects on meal size and on daily energy intake are at least partly

post-ingestively

mediated, since HF elicited greater intake when the orosensory stimuli

associated

with HF and HC were held constant.

In summary, previous single meal laboratory studies in which feeding was

externally

evoked had established that HF elicited larger meals than HC (Warwick and

Synowski,

1999 and Warwick et al., 2000). ... The present studies demonstrate that single

meal

paradigms yield results consistent with spontaneous feeding of high-fat and

high-carbohydrate liquid diets ...

Al Pater, PhD; email: old542000@...

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