2018 was a year of abundant research on the affects of different food sources on body weight management, body composition and insulin resistance. Let’s take a look at some of these studies.
In May a review of multiple clinical trials and observational studies found consistent evidence that eating a plant-based diet results in decreases in weight along with reduced blood pressure and lower risk of cardiovascular disease (1). In addition, plant-based diets were associated with the prevention and even the reversal of atherosclerosis, the build-up of plaque inside arteries that can lead to heart attacks and strokes.
June saw the publishing of a systematic review and meta-analysis of randomized controlled trials with the goal of updating the European Association for the Study of Diabetes (EASD) clinical practice guidelines for nutrition. Researchers examined evidence for the effect of vegetarian dietary patterns on blood sugar control, cholesterol level, body weight and BMI. Vegetarian patterns that met the eligibility criteria for this review included both completely plant-based diets of vegetables, fruits, whole grains, and legumes and lacto-ovo vegetarian diets that included some eggs and dairy products. Nine trials including 664 participants were included in this review and meta-analysis. Participants were middle-aged, overweight and diagnosed with type-2 diabetes. Results showed that vegetarian dietary patterns improve body weight and levels of stored body fat as well as blood sugar control and cholesterol levels (2).
In October a review of 11 controlled trials looking at dietary interventions for type-2 diabetes found that plant-based diets (where less than 10% of daily calories were derived from animal products) improved weight, cholesterol levels, symptoms of depression and diabetes control in people with type-2 diabetes (3). Average weight loss was 5.23 kg in the groups eating plant-based and 2.83 kg in the groups eating a control diet. Overall the plant-based groups found their diet highly acceptable and their adherence to it was greater than in those eating the control diets.
THE MOST NOTABLE STUDY ON WEIGHT LOSS OF 2018 (4):
In November a randomized clinical trial compared completely plant-based diets with control diets containing animal-sourced food for their affects on metabolic effects including weight loss, fat loss and insulin resistance. Seventy five overweight participants were recruited and were randomly assigned to either an exclusively plant-based vegan diet or a control diet. The plant-based vegan group followed a low-fat protocol consisting of vegetables, grains, legumes and fruits with no animal products or added oils. Daily fat intake in the vegan diet was 20 to 30 gm. The control group were asked to maintain their current diet, including animal products, for the duration of the study. The trial lasted sixteen weeks.
This study demonstrated that it is both the quality and the quantity of dietary protein from a plant-based vegan diet that are associated with improvements in body composition, body weight, and insulin resistance in overweight individuals.
The vegan group showed significant reductions in body weight with 6.5 more kilograms lost on average than in those eating the control diet.
Significant reductions in body mass index and body weight were only observed in the vegan group.
Similarly, fat mass and particularly visceral fat volume (the metabolically active and dangerous fat located around the organs in the lower abdomen) were reduced only in the vegan group.
This reduction in fat mass was linked to three factors;
The decrease in the intake of animal protein
The increase in the intake of plant protein
The change in the amino acid composition of the plant protein
Each gram reduction in animal protein intake was associated with a decrease in fat mass of 0.04 kg. The vegan group reduced their intake of animal protein by 36.2 g on average which was associated with a reduction in fat mass of 1.45 kg.
Each gram increase in plant protein intake was associated with a decrease in fat mass of 0.046 kg. The vegan group increased their intake of plant protein by 19.2 gm on average which was associated with a reduction in fat mass of 0.88 kg.
A decrease in intake of the amino acid leucine was associated with a reduction in fat mass of 0.82 kg.
Overall average decrease in fat mass in those on the vegan diet was 4.3 kg.
Only the vegan group showed significantly reduced insulin resistance.
A decrease in intake of the amino acid histidine was associated with a decrease in insulin resistance that was independent of changes in BMI and energy intake.
A decreased intake of five other amino acids (leucine, threonine, lysine, methionine and tyrosine) was also associated with reduced insulin resistance however these associations only appeared with loss of weight.
The vegan group reduced the intake of all six of these amino acids.
A DISCUSSION ABOUT ESSENTIAL AMINO ACIDS;
The building blocks of protein are amino acids. The proteins within human beings are made up of twenty different amino acids. Nine of these are essential amino acids, meaning that our bodies cannot produce them but need to acquire them from food. Essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Non-essential amino acids are those that our bodies can produce from the normal breakdown of proteins. Non-essential amino acids are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine (9).
Protein in the diet, especially protein that is high in essential amino acids, is a trigger for the release of insulin. Conversely higher intake of non-essential amino acids is linked to a decrease in insulin secretion and increased glucagon secretion, two factors that lead to appetite control and weight loss. Essential amino acids are found in greater concentration in animal proteins such as meats and dairy while plant proteins, though they do contain all the essential amino acids, are higher in non-essential amino acids (4).
As discussed above, the benefits of reducing the essential amino acids leucine and histidine are a decrease in fat mass (leucine) and a decrease in insulin resistance (histidine). Reductions in other amino acids can also be valuable. For example, the essential amino acid methionine and the non-essential amino acid, cysteine, were also reduced in the vegan group of this study. Cysteine and methionine are sulfur-containing amino acids. Several previous studies have shown that the restriction of sulfur-containing amino acids is beneficial in the prevention of chronic diseases such as cardiovascular disease, type-2 diabetes and cancer (5,6).
From this study we can conclude that lower intake of some essential amino acids is favourable for the health of human beings. But do people eating completely plant-sourced diets need to worry about getting enough of all of the essential amino acids? The answer is a definite “No!”. All plants contain at least some of every essential amino acid and a vegan diet consisting of a variety of plants will easily exceed the recommended daily intake for total protein and for each individual essential amino acid. Every human body maintains a pool of amino acids from which to build the specific proteins it needs. The old notion that certain protein foods must be eaten at the same time in order to produce complete proteins was disproven years ago (7,9).
It is interesting to note that quinoa, buckwheat, soy and peanuts do contain all nine essential amino acids. Common plant-sourced food combinations such as rice and beans and hummus and pita also provide all nine essential amino acids. Peanuts in fact contain all twenty of the amino acids found in human beings (10). But there is no need to even consider this when you choose your foods. If you eat a variety of plants you will get all the essential amino acids that you need.
On the other hand, intake of animal protein, a type of protein which contains all nine essential amino acids, is not associated with health benefits. Higher animal protein intake (20% or more of daily calories from animal protein) has been linked with a 73-fold increase in diabetes risk and a 74% increase in early death from all causes (8).
TO SUM UP…
Plant-sourced foods are a nutritious and efficient way to lose weight and body fat as well as to reduce insulin resistance. Both the quality and quantity of dietary protein play a role in these health improvements. Though this study could not definitively prove that the type of protein eaten is the sole driver behind these advantageous effects, it certainly infers causation. It demonstrates that plant protein intake, avoidance of animal protein and the reduction of certain amino acids play beneficial roles in regulating body weight, body composition, and insulin resistance. In practical terms, concentrating on eating plant foods is a logical step towards loss of weight in general and specifically loss of fat. And the bonus is that this same act can also lower insulin resistance, a risk factor for cardiovascular disease and diabetes.
1 Kahleová, H., Levin, S., Barnard, N.D. Vegetarian dietary patterns and cardiovascular disease. Prog Cardiovasc Dis. Published online May 29, 2018.
2 Viguiliouk, E., Kendall, C.W., Kahleová, H., Rahelić, D., Salas-Salvadó, J., Choo, V.L., Mejia, S.B., Stewart, S.E., Leiter, L.A., Jenkins, D.J., Sievenpiper, J.L. Effect of vegetarian dietary patterns on cardiometabolic risk factors in diabetes: A systematic review and meta-analysis of randomized controlled trials. Clin Nutr. 2018 Jun 13. pii: S0261-5614(18)30220-6.
3 Toumpanakis, A., Turnbull, T., Alba-Barba, I. Effectiveness of plant-based diets in promoting well-being in the management of type-2 diabetes: a systematic review. BMJ Open Diab Res Care Oct 20 2018; 6:e000534.
4 Kahleova, H., Fleeman, R., Hlozkova, A., Holubkov, R., Barnard, N.D. A plant-based diet in overweight individuals in a 16-week randomized clinical trial: metabolic benefits of plant protein. Nutr Diabetes. 2018;8:58-68.
5 Krajcovicova-Kudlackova, M., Babinska, K., Valachovicova, M. Health benefits and risks of plant proteins. Bratisl. Lek. Listy. 2005;106:231–234.
6 Dong, Z., Sinha, R., Richie, J.P. Disease prevention and delayed aging by dietary sulfur amino acid restriction: translational implications. Annals of the New York Academy of Sciences. 2018;1418(1):44–55.
7 Davis, B (RD), Melina, V. (RD). Becoming Vegan: The Complete Reference to Plant-Based Nutrition (Comprehensive Edition). Book Publishing Company. 2014.
8 Levine, M.E., et al. Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell. Metab. 2014;19:407–417.
10 Arya, S.S., Salve, A.R., Chauhan, S. Peanuts as functional food: a review. J Food Sci Technol. 2016 Jan; 53(1): 31–41.
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