Influence of increasing dietary protein on hepatic fat accumulation and postprandial metabolism.

Fat can accumulate, not only in the adipose tissue, but also in non-adipose
tissue like skeletal muscle and other organs like the liver. When lipid
accumulation exceeds the innate storage capacity of these tissues, so-called
lipotoxicity can develop and this can drive the inflammatory state associated
with obesity, and induce insulin resistance. Increased intra-hepatic lipid
(IHL) is correlated with hypertriglyceridemia as well as a reduced suppressive
effect of insulin on hepatic glucose production, which contributes to
hyperglycemia. Dietary manipulation can rapidly change lipid storage in
tissues. A recent human study showed that protein intake significantly blunted
the effect of a high-fat diet on IHL in healthy volunteers.

To investigate the potential beneficial effect of increasing protein in the
diet in order to decrease hepatic lipid accumulation on a high-fat diet.

A strictly-controlled dietary intervention study using a cross-over design with
two intervention periods will be performed in healthy volunteers (n=20).
Parallel to the groups in the cross-over design a control group will be
included in the study (n=10).

After a two-week run-in period on a low-protein, low-fat diet (according to the
healthy eating guidelines), subjects will be assigned to either one of the two
groups (high-fat group or the control group). The high-fat group consists of
two intervention periods of two weeks per diet, either high or low protein.
Half of the subjects assigned to the high-fat group will start on the
low-protein diet, the other half on the high-protein diet. After 2 weeks
subjects will cross to the other condition. The control group will continue on
the low-protein, low-fat diet for 4 weeks, and serve as a control. Tests will
be performed after 2, 4 and 6 weeks.

This study will require an effort of the subjects, since they have no freedom
to eat what they want for 6 weeks. This means that they will not be able to eat
out and that they cannot eat snacks during parties for instance. Besides, they
have to eat at the university during week days. Furthermore, in the 6 weeks of
the study they have to come to the hospital in Ede three times, of which two
times a whole day.
Risks for the subjects during this study are considered moderate.
The high-protein diets do not exceed safe levels of protein intake of 2.5
g/kg/d, since they will receive approximately 2.2 g/kg/d in the high protein
diet. Besides, subjects with known kidney problems or other medical issues will
not be included in the study. The subjects who will receive the high-fat diet
are likely to gain weight and to have increased hepatic fat after the
intervention. The hepatic fat accumulation is reversible and is not expected to
cause any health related problems. Hepatic fat content is very low in young,
lean, healthy subjects. Although the high-fat diet will increase liver fat,
absolute levels of liver fat will remain far below what is considered hepatic
steatosis (5% wet-weight).
Subjects will be checked 4 weeks after the intervention to see if they have
lost the gained weight. If they did not lose weight, counselling will be
offered.
The meal challenge with added stable isotopes tracers (13C-palmitate) is
frequently used in research of the postprandial fat handling. Stable isotopes
are naturally occurring isotopes and are not harmful for subjects, as there is
no decay.
Proton Spectroscopy (1H-MRS) is not considered to bare any additional risk for
the subject, as long as contra-indications are taken into account.
Adipose tissue biopsies will be taken, under local anaesthesia, by an
experienced physician, and proper precautions will be taken to minimize the
risk of complications. Taking an adipose tissue biopsy can generate mild
discomfort and result in local bruising.
Furthermore, placing a venous catheter and blood sampling can occasionally
cause a local haematoma or bruise and some participants may report pain or
discomfort.
The radiation of the DXA scanning is approximately 0.2 µSv, which is within
normal limits.

Subjects will get a financial compensation of ¤300,- when they complete the
study.