Obesity prevalence has nearly doubled between 1980 and 2014, and obesity increases the risk of
diseases, such as type II diabetes and cardiovascular diseases. Dietary modulation is the main
strategy applied as a part of primary and secondary prevention of obesity and obesity-associated
diseases, but an optimal diet to improve the success of weight loss maintenance has not reached
consensus among worldwide expects. During the last decade, it has been observed that the gut
microbiota composition is associated with obesity and obesity-associated diseases. However, a
deeper understanding of how the host metabolism is affected by dietary modulation of the gut
microbiota is necessarily before microbiota-based dietary recommendations can be applied as a
strategy for prevention and treatment of obesity and obesity-associated diseases.
The objective for this PhD thesis was to investigate how nutrition affects the gut and the
microbiome in relation to obesity and obesity-associated diseases. The objective was investigated
by the conduct of three studies (KIFU, PROKA, MNG). In KIFU, the effect of habitual calcium
intake on faecal fat and energy excretions was investigated by an observational study. The 189
participants collected faecal samples for five days and had a 1-day visit where metabolic markers
and anthropometric data were collected. In PROKA, the effect of protein supplementation (whey
with/without calcium and soy) on weight maintenance success was investigated by a randomised
controlled trial. 220 overweight and obese subjects went through an 8-week weight loss period
followed by a 24-week weight maintenance period. Measurements included anthropometry,
metabolic markers, appetite sensation and energy expenditure. In MNG, the effect of arabinoxylan
oligosaccharides (AXOS) and polyunsaturated fatty acid (PUFA) intakes on the gut microbiota
composition was investigated by a randomised cross-over study with two 4-week diets periods and
a 4-week washout period. Faecal samples and metabolic markers were collected from 30 subjects
before and after each diet period.
Results showed that habitual dietary calcium intake was not associated with faecal excretions of fat
and energy. However it was negatively associated with total and low density lipoprotein (LDL)
cholesterol concentrations and systolic blood pressure (BP) (Paper I). Protein supplementation
(whey with/without calcium or soy) did not improve success of weight maintenance or metabolic
markers, compared to carbohydrate in individuals with a normal protein intake, despite sustained
effects of appetite sensation and energy expenditure (Paper II). AXOS intake had bifidogenic
effects on the gut microbiota composition, and butyrate-producing bacteria were the main
contributors to the change of the bacterial community. Beneficial changes in metabolic markers
were not observed. PUFA intake did not alter gut microbiota composition, but improved systolic
and diastolic BP, and resulted in impaired glucose metabolism (Paper III).
In conclusion, the current evidence does not support that protein supplementation improves weight
maintenance after a weight loss, compared to carbohydrate, in individuals with a normal protein
intake. Convincing evidence supports that dietary calcium intake improves BP and lipid profile,
while an effect on faecal fat and energy excretion in the free living population remains inconclusive.
AXOS intake can increase abundance of Bifidobacteria and may stimulate the abundance of
butyrate producers, whereas the effect of fat quality on gut microbiota modulation is inconclusive
due to the limited literature.