Fruit Flies

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Exp Gerontol. Author manuscript; available in PMC 2008 December 22.

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Published in final edited form as:
Exp Gerontol. 2007 March ; 42(3): 247–251. doi:10.1016/j.exger.2006.10.009.

Counting Calories in Drosophila Diet Restriction
Kyung-Jin Min1, Thomas Flatt1, Indrek Kulaots2, and Marc Tatar1
1 Department of Ecology andEvolutionary Biology, Brown University, Providence, RI 02912 USA
2 Division of Engineering, Brown University, Providence, RI 02912 USA

Abstract

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The extension of life span by diet restriction in Drosophila has been argued to occur without limiting
calories. Here we directly measure the calories assimilated by flies when maintained on full- and
restricted-diets. Wefind that caloric intake is reduced on all diets that extend life span. Flies on lowyeast diet are long-lived and consume about half the calories of flies on high yeast diets, regardless
of the energetic content of the diet itself. Since caloric intake correlates with yeast concentration and
thus with the intake of every metabolite in this dietary component, it is premature to conclude forDrosophila that calories do not explain extension of life span.

Keywords
diet restriction; calorie restriction; nutrition; aging; life span; Drosophila

1. Introduction

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Reduced food intake without malnutrition extends life span in many organisms including yeast,
nematode, fruit fly, and rodents (Koubova and Guarente, 2003; Masoro, 2000; Partridge et al.,
2005). Inrodents, reduced intake of total calories extends life span, yet limiting specific
nutrients can also increase survivorship (Miller et al., 2005; Yu and Masoro, 1985; Zimmerman
et al., 2003). It is a current debate as to whether limiting calories is a feature of nutrition
responsible for extended life span in the fruit fly, Drosophila melanogaster. In recent work to
address this question Mairet al. (2005) simultaneously manipulated dietary yeast and sugar to
vary nutrient quality and caloric value. Survivorship was increased substantially on diets that
restricted yeast while holding sugar constant, while life span changed little when sugar was
restricted in diets with a constant amount of yeast. Notably, Mair et al. reasoned that the actual
caloric intake was equal for femalesgiven diets with equal energetic value because solitary
test females extend their proboscis for equal durations. Since females on isocaloric diets with
low yeast are longer lived than those on high yeast, the authors argue that diet restriction (DR)
mediates life span because it limits specific nutrient components of yeast rather than calories.
The conclusion of Mair et al. requires actualcaloric intake to be proportional to the energetic
content of the diet media. However, the relationship between proboscis extension and nutrient
intake is unknown, and recent studies confirm that food intake may not be constant across diets

1 Correspondence: Marc Tatar, Department of Ecology and Evolutionary Biology, Brown University, Box G-W, Providence, RI 02912
USA, Tel. 401-863-3455, Fax.401-863-2166, E-mail: Marc_Tatar@brown.edu.
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Min et al.

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that vary in yeast or sugar concentration (Carvalho et al., 2005; Min and Tatar, 2006a). Females
are seen to both increase and decrease the rate of intake when fed a restricted diet. It is thus...