Healthy ageing is associated with a reduction in appetite and food intake, including protein intake, which predisposes older people to loss of body weight and in particular, skeletal muscle mass.
A common strategy to increase energy intake and body weight in undernourished older people is the use of >25–30 g whey protein-enriched supplements which aim to result in preserved or even increased muscle mass and strength. Whereas in healthy, younger adults, protein is considered to be the most satiating macronutrient and protein-rich supplements and diets are often recommended as a weight loss strategy in obese, younger individuals.
The researchers of the current study have previously reported that in older adults the acute suppression (up to three hours following ingestion) of energy intake caused by protein supplementation is less than that observed in younger adults, resulting in an increase of overall energy and protein intake in the older adults.
In this study, the team of researchers from Royal Adelaide Hospital, Australia, aimed to characterise the effect of ageing on the suppression of food intake at breakfast, lunch, and dinner over a time period of nine hours by a pre-breakfast whey protein load (30 g and 70 g), compared to a control drink in healthy younger and older men, using a sample size of 30.
The team report that, overall, suppression of energy intake by whey protein was less in healthy older men: −94 ± 82kcal when compared to younger men −169 ± 100 kcal and cumulative protein intake was increased in both groups with the addition of the protein drink.
They hypothesised that suppression of energy intake by whey protein when compared to control would be less in healthy older than younger adults, resulting in an increase in cumulative energy and protein intake in the older men.
They found that cumulative protein intake was increased when volunteers consumed the protein drinks. Consumption of 30g whey protein led to a 17% increase while 70 g whey protein led to 36% increase in the younger group. In the older group, consumption of 30g whey protein led to 23% increase and 70g whey protein led to 47% increase.
They conclude: "These findings support the use of whey-protein drink supplements in healthy older patients who aim to increase their protein intake without decreasing their overall energy intake."
The study included 15 healthy younger men (mean age: 27 ± 1 years) and 15 healthy older men (75 ± 2 years).
Each participant was studied on three occasions, separated by ~3–10 days. On each occasion, they were given a standardised meal the night before, and informed not to drink alcohol or take part in strenuous exercise for 24 hours. They attended the lab in the morning and received a single drink of either flavoured water (control; ~2 kcal), 30 g whey protein (120 kcal), or 70 g whey protein (280 kcal). The drinks were all around 450 mL with different quantities of food-grade unflavoured whey protein isolate (Bulk Nutrients) dissolved in varying amounts of water.
Before having the drink, perceptions of appetite were assessed by visual analogue scales (VAS) and the antral area of the stomach. Subsequently, the drink was served in an opaque cup to ensure that the volunteers were blinded. Following consumption of the drink (8.30am), palatability of the drink and perceptions of appetite were assessed by VAS. The antral area of the stomach was measured at several time points between the drink and breakfast. Energy intake was measured at breakfast, lunch, and dinner (5 p.m.).
Energy intake after the drink was suppressed more by whey protein compared to control and suppression of energy intake by the 70 g whey protein compared to control was greatest at lunch. The protein drink did not affect energy intake at dinner in either age group.
Older compared to younger men had a lower desire to eat but also lower fullness throughout the day, suggesting that older people experience lower sensitivity of the appetite-suppressing effects of a protein drink and may have a decreased perception of gastric distension as seen in our previous study.
Cumulative energy intake on the protein days compared to control was slightly higher in older (+4%) than younger men (−1%).
The findings suggest that the use of protein shakes to suppress appetite may not be an effective method for reducing energy intake but this may well be due to the fact the volunteers in this study were not trying to lose weight.
"The insignificant effect of the whey drink on cumulative daily energy intake in this study may indicate that the ingestion of a single daily dose of whey protein, in doses up to 70 g, is unlikely to be a successful weight loss strategy to achieve a negative energy balance, without taking the effects on energy expenditure and muscle anabolism into account. Even if whey protein was given more than once a day, we have no evidence that this would have resulted in a greater cumulative energy deficit, particularly in older adults.
"The energy content of the protein drink would have equalled or outweighed suppression of energy intake produced by the protein drink. Given our finding with one protein drink before breakfast, it is likely that suppression of cumulative energy intake with multiple drinks would have been even less.
"The subjects in this study were not aware, however, that we were interested in or measuring their ad libitum meal energy intake throughout the day in response to the different drinks. Young adults using protein supplements to lose weight may have different responses to those in this study....
"The suppressive effect of whey protein in younger adults may be affected by having dietary restraints or actively trying to lose body weight. Furthermore, the overall suppressive effect of protein supplements may be influenced by protein supplement intake before each meal of the day."
The authors note the limitations of this study include the small sample size and the use of only male volunteers.
Soenen. S., et al
"Whey Protein Drink Ingestion before Breakfast Suppressed Energy Intake at Breakfast and Lunch, but Not during Dinner, and Was Less Suppressed in Healthy Older than Younger Men"