Satiety: Stuffed with Protein

Evidence continues to mount on the ability of a high-protein meal to promote satiety, at least in the short term. However, one recent study opened the door to questions on the exact mechanism of a high-protein meal's effect on satiety, reporting such a lunch did not appear to act via influence on hunger hormones such as ghrelin, GLP-1 and PYY.¹

However, previous data certainly demonstrated high-protein meals can affect these hormones and influence satiety. In 2006, researchers from The Netherlands reported a high-protein breakfast more effectively decreased postprandial ghrelin concentrations than did a high-carb breakfast.² There was a particularly strong association between ghrelin and glucose-dependent insulinotropic polypeptide and glucagon, suggesting stimulation of these peptides may mediate the postprandial ghrelin response.

The key to protein's effect on satiety could be in the timing of the meal. A group of Purdue University scientists investigated the effects on satiety of high-protein meals given throughout the day, finding such a meal at breakfast had the greatest positive effect on satiety.³

A great deal of research on protein and satiety has sought to differentiate between various types or origins of protein. A University of Toronto study found whey, soy and gluten preloads in both lean and overweight boys decreased food intake up to three hours later, compared to glucose preload.⁴ They concluded postprandial ghrelin, GLP-1, insulin and CCK may contribute to this post-protein satiety, noting GLP-1 concentrations were increased in overweight subjects, possibly contributing to satiety responses in this group.

A similar comparison was completed on casein and whey, involving overweight men taking preloads of either casein, whey, lactose or glucose, and tested for plasma ghrelin, CCK, insulin, glucose and amino acids, gastric emptying rate (plasma paracetamol), appetite rating (visual analog scale), and ad libitum energy intake.⁵ Results showed CCK was 71-percent higher 90 minutes after the protein preloads, compared with glucose and lactose; this translated to increased satiety and reduced appetite.

On its own, casein has demonstrated an effect on satiety. A University of Maastricht, Netherlands, trial pitting a high-casein against a low-casein diet reported the higher-casein meal (25-percent protein) resulted in higher energy expenditure and sleeping metabolic rate.⁶ Overall, satiety was 33-percent higher in the 25-percent group than in the 10-percent casein group.

High- and low-soy protein meals were also compared in recent research from University of Maastricht.⁷ Reporting similar results, researchers said the high-soy meal (25 percent protein) was more satiating than the 10-percent soy meal, after measuring for levels of various hunger hormones as well as insulin and the amino acid taurine.

Looking deeper into the reasons why protein is so satiating, Maastricht scientists recently tested various protein meals to gain insight on the role tryptophan may play in protein satiety.⁸ Compared to protein meals with either gelatin or gelatin-plus-tryptophan, the protein meal featuring lactalbumin—a high-tryptophan compound found in whey or milk—suppressed hunger the most at four hours after the meal, although the researchers were not able to credit any differences in tryptophan for the results.

Another component of whey and casein gaining scientific attention is glycomacropeptide (GMP). In 2009, Maastricht researchers compared whey meals with or without GMP content in healthy subjects, finding the whey with GMP breakfast decreased energy intake at lunch more than in the whey without GMP group.⁹

University of California, Berkeley, researchers tested several different combinations of whey, whey protein isolate and glycomacropeptide on satiety and CCK levels in both men and women.¹⁰ They found satiety was greater after whey protein preloads compared to control and glycomacropeptide-only preloads in women, but not in men. They concluded GMP alone is not critical in pre-meal, whey-induced satiety, but may have a unique role in compensatory intake regulation managing daily energy intake.

A 2006 proprietary trial on a glycomacropeptide-based ingredient (as Satietrol®, from PacificHealth Laboratories) found a significant reduction (20 percent) in food intake in overweight subjects with an average body mass index (BMI) of 28.

A protein extract from potatoes (as Slendesta™, from Kemin Health) is also theorized to help control hunger via CCK mechanism, and proprietary studies conducted at Iowa State University have shown proteinase inhibitor II (PI2) from Slendesta promotes satiety and weight loss. One study found participants taking Slendesta before a meal experienced significantly greater fullness and a decreased motivation to eat. In fact, CCK levels rose and remained elevated for a longer period of time post meal in those taking Slendesta than in the placebo group. In another Iowa State study, Slendesta supplementation led to statistically significant reductions in weight, waist and hip measurements in participants consuming either 300 mg/d or 600 mg/d of Slendesta (providing 15 mg or 30 mg PI2, respectively) for 12 weeks.

References on the next page ...

References for "Satiety: Stuffed with Protein"

1. Smeets AJ et al. "Energy Expenditure, Satiety, and Plasma Ghrelin, Glucagon-Like Peptide 1, and Peptide Tyrosine-Tyrosine Concentrations following a Single High-Protein Lunch." J Nutr. 2008;138:698-702.

2. Blom WA et al. "Effect of a high-protein breakfast on the postprandial ghrelin response." Amer J Clin Nutr. 2006; 83(2):211-20.

3. Leidy HJ et al. "Increased dietary protein consumed at breakfast leads to an initial and sustained feeling of fullness during energy restriction compared to other meal times." Br J Nutr. 2009 Mar;101(6):798-803.

4. Bowen J et al. "Appetite regulatory hormone responses to various dietary proteins differ by body mass index status despite similar reductions in ad libitum energy intake." J Clin Endocrinol Metab. 2006;91(8):2913-9.

5. Bowen J et al. "Energy intake, ghrelin, and cholecystokinin after different carbohydrate and protein preloads in overweight men." J Clin Endocrinol Metab. 2006 Apr;91(4):1477-83.

6. Hochstenbach-Waelen A et al. "Comparison of 2 diets with either 25% or 10% of energy as casein on energy expenditure, substrate balance, and appetite profile." Am J Clin Nutr. 2009 Mar;89(3):831-8.

7. Hochstenbach-Waelen A et al. "Effects of high and normal soyprotein breakfasts on satiety and subsequent energy intake, including amino acid and 'satiety' hormone responses." Eur J Nutr. 2009 Mar;48(2):92-100.

8. Hochstenbach-Waelen A et al. "Acute effects of breakfasts containing alpha-lactalbumin, or gelatin with or without added tryptophan, on hunger, 'satiety' hormones and amino acid profiles." Br J Nutr. 2008 Nov 19:1-8. Epub ahead of print.

9. Hochstenbach-Waelen A et al. "Effects of complete whey-protein breakfasts versus whey without GMP-breakfasts on energy intake and satiety." Appetite. 2009 Apr;52(2):388-95.

10. Burton-Freedom BM. "Glycomacropeptide (GMP) is not critical to whey-induced satiety, but may have a unique role in energy intake regulation through cholecystokinin (CCK)." Physiol Behav. 2008 Jan 28;93(1-2):379-87.