No effect of salmon fish protein on 2-h glucose in adults with increased risk of type 2 diabetes: a randomised controlled trial

Protein-based nutritional strategies to manage the development of diabetes: evidence and challenges in human studies

Type 2 diabetes mellitus (T2DM) is one of the most prevalent diseases in modern society, governed by both genetic and environmental factors, such as nutritional habits. This metabolic disorder is characterized by insulin resistance, which is related to high blood glucose levels, implying negative health effects in humans, hindering the healthy ageing of people. The relationship between food and health is clear, and the ingestion of specific nutrients modulates some physiological processes, potentially implying biologically relevant changes, which can translate into a health benefit. This review aims to summarize human studies published in which the purpose was to investigate the effect of protein ingestion (in native state or as hydrolysates) on human metabolism. Overall, several studies showed how protein ingestion might induce a decrease of glucose concentration in the postprandial state (area under the curve), although it is highly dependent on the source and the dose. Other studies showed no biological effects upon protein consumption, mostly with fish-derived products. In addition, the major challenges and perspectives in this research field are highlighted, suggesting the future directions, towards which scientists should focus on. The dietary intake of proteins has been proven to likely exert a beneficial effect on diabetes-related parameters, which can have a biological relevance in the prevention and pre-treatment of diabetes. However, the number of well-designed human studies carried out to date to demonstrate the effects of specific proteins or protein hydrolysates in vivo is still scarce.

Dietary Consumption on Glycemic Control Among Prediabetes: A Review of the Literature

Introduction

Prediabetes is a condition that, if left unaddressed, can lead to various complications, such as neuropathy, retinopathy, and nephropathy. Among the critical factors contributing to the development of type 2 diabetes mellitus, dietary choices stand out as particularly significant.

Objective

Consequently, our objective is to examine the latest research findings concerning dietary consumption and its impact on glycemic control in individuals with prediabetes.

Methods

A literature review of randomized controlled trials was performed using databases such as PubMed, Scopus, and ScienceDirect with searches conducted from January 2019 to 2023. The primary reviewer assessed the quality of the selected studies for bias risk using the Joanna Briggs Institute critical appraisal method for randomized controlled trials. Initially, 975 articles were identified through the search, but after applying the inclusion criteria, only 9 articles were ultimately selected.

Results

The review found that a carrageenan-free diet, yogurt with Lactobacillus plantarum OLL2712, Allium hookeri extract (AHE), and delta-tocotrienol improve HbA1C levels. However, salmon, zinc supplement, and balanced deep-sea water were not effective on HbA1C. In addition, studies on the effectiveness of vitamin D in controlling blood glucose levels are inconsistent.

Conclusion

Nurses can enhance patient outcomes through collaborative efforts to create individualized dietary strategies. These strategies may encompass the adoption of a carrageenan-free diet, the inclusion of L plantarum OLL2712-enriched yogurt, the utilization of AHE, and the integration of delta-tocotrienol into the dietary plan. This approach is particularly applicable to ambulatory care nurses, health supervisors, and primary care providers.

Glycated Proteins, Glycine, Acetate, and Monounsaturated Fatty Acids May Act as New Biomarkers to Predict the Progression of Type 2 Diabetes: Secondary Analyses of a Randomized Controlled Trial

Food protein or food-derived peptides may regulate blood glucose levels; however, studies have shown inconsistent results. The aim of the present study was to characterize subgroups of individuals with increased risk of type 2 diabetes (T2D) and to investigate the cardiometabolic effects of fish protein in the same subgroups. We first divided participants into high insulin_iAUC and low insulin_iAUC subjects based on their insulin incremental area under the curve (iAUC) levels after a 2 h oral glucose tolerance test (OGTT), and secondly based on whether they had received 5.2 g salmon fish protein or placebo for 8 weeks, in a previously conducted randomized controlled trial (RCT). We then profiled these groups by analyzing plasma metabolomics and peripheral blood mononuclear cell (PBMC) gene expression. Compared to the low insulin_iAUC group, the high insulin_iAUC group had higher plasma concentrations of monounsaturated fatty acids (MUFAs) and glycated proteins (GlycA) and lower concentrations of glycine and acetate. After intervention with fish protein compared to placebo, however, only acetate was significantly increased in the low insulin_iAUC group. In conclusion, we identified metabolic biomarkers known to be associated with T2D; also, intervention with fish protein did not affect cardiometabolic risk markers in subgroups with increased risk of T2D.

Consumption of salmon fishmeal increases hepatic cholesterol content in obese C57BL/6 J mice

PURPOSE

By-products from farmed fish contain large amounts of proteins and may be used for human consumption. The purpose of this study was to investigate cardiometabolic effects and metabolic tolerance in mice consuming fishmeal from salmon by-products, salmon filet or beef.

METHODS

Female C57BL/6J mice were fed chow, as a healthy reference group, or a high-fat diet for 10 weeks to induce obesity and glucose intolerance. Obese mice were subsequently given isocaloric diets containing 50% of the dietary protein from salmon fishmeal, salmon filet or beef for 10 weeks. Mice were subjected to metabolic phenotyping, which included measurements of body composition, energy metabolism in metabolic cages and glucose tolerance. Lipid content and markers of hepatic toxicity were determined in plasma and liver. Hepatic gene and protein expression was determined with RNA sequencing and immunoblotting.

RESULTS

Mice fed fishmeal, salmon filet or beef had similar food intake, energy consumption, body weight gain, adiposity, glucose tolerance and circulating levels of lipids and hepatic toxicity markers, such as p-ALT and p-AST. Fishmeal increased hepatic cholesterol levels by 35-36% as compared to salmon filet (p = 0.0001) and beef (p = 0.005). This was accompanied by repressed expression of genes involved in steroid and cholesterol metabolism and reduced levels of circulating Pcsk9.

CONCLUSION

Salmon fishmeal was well tolerated, but increased hepatic cholesterol content. The high cholesterol content in fishmeal may be responsible for the effects on hepatic cholesterol metabolism. Before introducing fishmeal from salmon by-products as a dietary component, it may be advantageous to reduce the cholesterol content in fishmeal.

Postprandial Effects of Salmon Fishmeal and Whey on Metabolic Markers in Serum and Gene Expression in Liver Cells

Fish is considered an important part of a healthy diet, in part due to the content of long chain omega-3 fatty acids. However, both lean and fatty fish have beneficial health effects, suggesting that micronutrients and proteins may play a role. In a randomised, controlled, cross-over trial, five healthy male participants consumed 5.2 g of protein from either salmon fishmeal or whey. Blood samples were taken before and 30 and 60 min after intake. The concentration of glucose, lipids, hormones and metabolites, including 28 different amino acids and derivatives, were measured in serum or plasma. Cultured HepG2 cells were incubated with or without serum from the participants, and transcriptomic profiling was performed using RNA sequencing. The ingestion of both salmon fishmeal and whey reduced the glucose and triglyceride levels in serum. Protein intake, independent of the source, increased the concentration of 22 amino acids and derivatives in serum. Fishmeal increased the concentration of arginine, methionine, serine, glycine, cystathionine and 2-aminobutyric acid more than whey did. Incubation with postprandial serum resulted in large transcriptomic alterations in serum-fasted HepG2 cells, with the differential expression of >4500 protein coding genes. However, when comparing cells cultivated in fasting serum to postprandial serum after the ingestion of fishmeal and whey, we did not detect any differentially regulated genes, neither with respect to the protein source nor with respect to the time after the meal. The comparable nutrigenomic effects of fishmeal and whey do not change the relevance of fish by-products as an alternative food source.

Salmon fish protein supplement increases serum vitamin B12 and selenium concentrations: secondary analysis of a randomised controlled trial

Purpose

The main aim of the present study was to examine the effect of a fish protein supplement made from by-products from production of Atlantic salmon, on blood concentration of micronutrients.

Methods

We conducted an 8-week double-blind parallel-group randomised controlled trial. In total, 88 adults were randomised to a salmon fish protein supplement or placebo, and 74 participants were included in the analysis of vitamin D, omega-3, vitamin B12, selenium, folate, zinc, homocysteine and mercury.

Results

During the intervention period, geometric mean (GSD) of serum vitamin B12 concentrations increased from 304 (1.40) to 359 (1.42) pmol/L in the fish protein group (P vs. controls = 0.004) and mean (SD) serum selenium increased from 1.18 (0.22) to 1.30 (0.20) μmol/L (P vs. controls = 0.002). The prevalence of low vitamin B12 status (B12 < 148–221 > pmol/L) decreased from 15.4 to 2.6% in the fish protein group, while increasing from 5.9 to 17.6% in the placebo group (P = 0.045). There was no difference between the groups in serum levels of the other micronutrients measured.

Conclusion

Including a salmon fish protein supplement in the daily diet for 8 weeks, increases serum vitamin B12 and selenium concentrations. From a sustainability perspective, by-products with high contents of micronutrients and low contents of contaminants, could be a valuable dietary supplement or food ingredient in populations with suboptimal intake.

Trail Registration

The study was registered at ClinicalTrials.gov (ID: NCT03764423) on June 29th 2018.