Impact of fat co-ingestion with protein on the post-prandial anabolic response in elderly men

The progressive loss of skeletal muscle mass with aging, or sarcopenia, has a
major impact on our healthcare system due to increased morbidity and greater
need for hospitalization and/or institutionalization. The age-related loss of
skeletal muscle mass is facilitated by a combination of factors, which include
a less than optimal diet and a sedentary lifestyle. These factors contribute to
a disruption in the regulation of skeletal muscle protein turnover, leading to
an imbalance between muscle protein synthesis (MPS) and degradation. One way to
overcome this problem is to improve dietary intake of the elderly. It has been
well established that nutrient intake greatly affects protein turnover in
skeletal muscle tissue. Ingestion of dietary protein stimulates MPS rates and
inhibits muscle protein breakdown rates, resulting in an overall positive net
protein balance in both the young and elderly. However, it is not clear what
the impact is of fat co-ingestion with protein on digestion and absorption
kinetics or MPS rates in the healthy elderly men. A study performed by Elliot
et al. investigated the effect of whole milk ingestion on net muscle protein
balance after resistance exercise using an arteriovenous balance approach.
Ingestion of whole milk (containing 50 en% fats) stimulated the post-exercise
net uptake of phenylalanine and threonine to a greater extent than ingestion of
fat-free milk (containing 6 en% fat). Although, amino acid uptake is indicative
of *muscle anabolism*, it is not a direct measure of MPS so no firm conclusions
can be deduce from this work. Furthermore, milk also contains a certain amount
of carbohydrates (fat-free milk 55 en% and whole milk 30 en%), which does not
allow for direct assessment of fat co-ingestion per se. In the present st

The primary objective of this study is to investigate the effect of a single
meal-like amount of protein with or without fat on postprandial muscle protein
synthesis in healthy elderly men. Furthermore, as a secondary objective, we
will assess digestion and absorption kinetics.

Double-blind randomized intervention study

One group (n=12) will consume a test beverage of 350 mL containing 20 g of
intrinsically labeled casein, and the other group (n=12) will consume a
beverage of the same volume containing 20 g of casein plus 20 g of fat.

The burden and risks associated with participation are small. Insertion of the
catheters is comparable to a blood draw and could result in a small hematoma.
Muscle biopsies will be taken under local anesthesia by an experienced
physician, but may cause some minor discomfort for maximally up to 24 h after
completion. The discomfort is comparable to muscle soreness or the pain one has
after bumping into a table. We will take 5 and 19 blood samples (8 mL) during
the screening and experimental trial respectively. The total amount of blood we
draw is less than half the amount of a blood donation and will be completely
restored in approximately 1 month. Participants come to the university twice: 1
screening (4 hours) and 1 experimental trial (entire day). For both the
screening and the experimental trial, participants have to be fasted, so they
are not allowed to eat and drink (except for water) from 22h00 the evening
before. Also, 3 days prior to the experimental trial participants should keep
their diet as constant as possible, do not perform any type of intense physical
exercise, and do not consume alcohol. During the screening we will perform a
DEXA and CT scan and an OGTT. Furthermore, we will ask the participants to fill
out a medical questionnaire and record their food intake for 2 days prior to
the experimental trial. During the experimental trial, we will collect muscle
and blood samples, and participants have to consume a test beverage consisting
of milk protein with or without milk fat. The intrinsically labeled milk
protein and milk fat has been approved for human consumption and has been used
in previous METC approved studies. There is no direct benefit for the
participants, only their contribution to scientific knowledge and nutritional
strategies that prevent muscle loss in the elderly, which will be obtained from
this study and used in the future.