Obese rats eating raw kidney beans lose body fat

Doug Skrecky (oberon@vcn.bc.ca)
Tue, 2 Jun 1998 09:25:56 -0700 (PDT)

British Journal of Nutrition 79: 213-221 1998

"Lipid Accumulation in Obese Zucker rats is Reduced by Inclusion of Raw
Kidney Bean (Phaseolus vulgaris) in the Diet"


The effects of inclusion of different levels of raw kidney bean
(Phaseolus vulgaris) of high lectin content (27 g/kg meal) in a
high-quality (lactalbumin control diet were tested in nutritional trials on
the growth and metabolism of obese Zucker (fafa) rats and their lean
littermates in comparison with pair-fed controls. All diets contained 100 g
total protein/kg and either 50 g lipids/kg (low fat) or 150 g lipids/kg
(moderate fat). The growth of both obese and lean rats on bean diets was
retarded by the daily bean intake in a dose-dependent manner. However, most
of this was because bean-fed rats contained less body fat than the controls
after 10 d. Thus, after feeding low-fat diets containing up to 130 g kidney
bean/kg (lectin intake <=0.2 g/kg body weight (BW) per d) in both 10 d and
70 d trials, the bodies of obese rats contained less fat but not protein
than their pair-fed controls. Moreover, by increasing the lipid content of
the diet to 150 g/kg, the level of bean inclusion could be increased to 280
g/kg (lectin intake >=0.4 g/kg BW per d) without loss of body protein and
skeletal muscle. Although these rats contained more body fat than those
which were fed on low-fat diets, their weight reduction could be accounted
for exclusively by reduced lipid content. In contrast, significant body
protein loss occurred when the same diet of high lectin content was fed to
lean littermates. Plasma insulin levels were significantly depressed in the
obese Zucker rats on bean diets but the pancreas was not significantly
enlarged nor its insulin content changed in 10 d trials. However,
significant pancreatic growth occurred on long-term (70 d) bean feeding
compared with pair-fed controls. The results suggest that, in addition to
animal nutrition, it may also be possible to use the bean lectin as a
dietary adjunct or therapeutic agent to stimulate gut function and
ameliorate obesity if a safe and effective dose-range can be established
for human subjects.

Additional quote from text of report:

As shown previously, the inclusion of high amounts of kidney bean
phytohaemagglutinin, its main physiologically active lectin component, in
the diet of young actively growing conventional rats at levels of 0.4 g/kg
BW per d or more, adversely affects their growth and metabolism. It causes
a major reduction in their body fat but the accompanying high catabolic
protein loss makes this an unacceptable means of weight reduction. However,
phytohaemagglutinin is not harmful for germ-free rats, therefore the weight
and muscle losses are not direct lectin effects but rather the consequence
of the damage caused by the phytohaemagglutinin-induced E. coli overgrowth
in the small intestine. As this is negligible at daily phytohaemagglutinin
intakes below 0.2 g and particularly below 0.1 g lectin/kg BW,
phytohaemagglutinin is essentially harmless even in conventional rats at
such low intakes.