The cons of a high-protein diet

Liesbet Delport and Marinda Venter unpack the cons of a high-protein diet for people living with diabetes and offers the Smart Health Diet as the alternative.

A healthy gut

There is a myth that a high-protein diet is the best way people living with diabetes need to eat to get their blood glucose under control and to improve their health.

High-protein diets are low in fibre and most people with diabetes don’t have a healthy gut, due to limited fibre intake. A type of fibre, called prebiotics, is found in wholegrains, fruit, vegetables and legumes (collectively called functional foods). There is ample evidence of good blood glucose control and improved insulin sensitivity on high-fibre diets based on wholegrains.

For a gut that is soft-stool friendly, you also need the right, good bacteria to be active and flourishing in your gut, creating a healthy microbiome for nutrient absorption and regular soft stools. This good bacteria, called probiotics, is common in fermented dairy like yoghurt, as well as other fermented foods and they live on fibre. Without fibre they wane and so your gut health will wane with it.

On average, the recommended fibre intake per day is 30-35g, chosen from a variety of fibres as they don’t have the same properties. Constipation is often a symptom of a fibre poor diet.

Colorectal cancer

Sixty percent of the body’s immunity is situated in the gut, but apart from protection against colds and flu, a healthy gut is of utmost importance for protection against various cancers, especially colorectal cancer.3 There is convincing evidence that a diet high in red meat and alcohol predisposes to colorectal cancer, whereas a diet high in fibre and rich in calcium protects from colorectal cancer.4

So, although your diet needs to include plenty of vegetables and fruit, the bare minimum is at least three servings of wholegrains per day. Calcium’s best source is low-fat dairy products and again you need at least three servings per day.4

The myth

A high-protein diet for good glycaemic control is a myth, because the benefits of going high on protein and low on carbs will only last for a couple of hours. Protein and fat take longer than carbs to digest and your blood glucose will start to show the effect after two to three hours when the carbs have come and gone.1 This will happen after every high-protein (and/or high-fat) meal.

Many people who have diabetes develop kidney problems (±30%) as high blood glucose levels cause damage to the kidney’s cells, just like it can cause damage to the cells of the retina in the eyes (causing blindness) and/or the cells of your nervous system, referred to collectively as microvascular damage. High-protein meals put more strain on your kidneys, as more protein in the bloodstream forces them to work much harder to get rid of waste products.

Many people with diabetes are sent to a dietitian by their doctor to place them on a low-protein diet, as their kidneys can’t cope anymore. The high-protein approach could fast forward you to chronic kidney disease. Serious circulation problems, due to damage to nerve cells are also common amongst the diabetic community and often end badly with amputations.

Pancreatic function

Taking care of your pancreatic function is at the essence of diabetic self-care. Insulin, which controls blood glucose levels, is excreted by the pancreas. Too much glucose in your blood causes your pancreas to work overtime and after weeks, month or years it gets tired and can’t cope. But it’s not only sugar and high-GI or refined carbohydrates that taxes the pancreas, protein and fat does too.5 So, changing from too much refined carbs to too much protein and/or fatty foods and shakes is like exchanging one bad habit for another.

Type 1 diabetic patients have been found to need extra insulin when they eat high-protein and/or high-fat meals, instead of balanced meals.1 Balanced meals would typically be what you would find in the Mediterranean diet4 or what is promoted in the South African equivalent, the Smart Health diet.

High-protein diets have also been shown to increase LDL cholesterol (bad cholesterol).6 With all the risks of microvascular damage that people with diabetes have to avoid, a high cholesterol level is an unwanted problem. High LDL cholesterol can lead to atherogenesis, which is the main cause of macrovascular damage, leading to heart attacks and stroke. In contrast, wholegrains, legumes, with the addition of fruit and vegetables, are providing soluble fibre which aids in lowering cholesterol.

The diet solution

The diet solution is to have a balanced meal plan (like the Smart Health Diet) that includes healthy functional foods and eliminates all unhealthy foods. As a person with diabetes, it’s best to consult a registered dietitian to explain the detail to you. In the meantime, have a look at and use the figure below as a guide to have a healthy meal.


  1. Smart, C.E.M., Evans, M, O’Connell, S.M., Mcelduff, P. Lopez, P.E., Jones, T.W., Davis, E.A. and King, B.R. Both dietary protein and fat increase postprandial glucose excursions in children with type 1 diabetes and the effect Is additive. Diabetes Care 2017;36:3897–3902.
  2. Küster-Boluda I., Vidal-Capilla I. Consumer attitudes in the election of functional foods. Spanish J. Mark. ESIC. 2017;21:65–79. doi: 10.1016/j.sjme.2017.05.002.
  3. 3. Tayyem, R.F., Bawadi, H.A., Shehadah, I.N., Suhad, S.A., Agraib, L.M., Bani-Hani, K.E., Tareq, A., Al-Nusairr, M., and Heath, D.D. Macro- and micronutrient consumption and the risk for colorectal cancer among Jordanians. Nutrients2015;7(3):1769-1786.
  4. 4. Sajesh K.V., Wong, T.Y., Loo Y.S., et al. Role of Diet in Colorectal Cancer Incidence. Umbrella Review of Meta-analyses of Prospective Observational Studies. JAMA Network Open. 2021;4(2):e2037341.
  5. Bell, K.J., Gray, R., Munns, D., Petocz, P., Howard, G., Colagiuri, S., and Brand-Miller, J.C. Estimating insulin demand for protein-containing foods using the food insulin index. Eur Jnl Clin Nutr 2014;68:1055-1059.
  6. McMillan-Price, J., Petocz, P., Atkinson, F., O’Neill, K., Samman, S., Steinbeck, K., Caterson, I. and Brand-Miller, JC. Comparison of 4 Diets of Varying Glycemic Load on Weight Loss and Cardiovascular Risk Reduction in Overweight and Obese Young Adults. Arch Intern Med. 2006;166:1466-1475.
Liesbet Delport


Liesbet Delport is a registered dietitian with a private practice in Mpumalanga. She is one of the founder members and research and development manager of the Glycemic Index Foundation of South Africa (GIFSA), founded in 1999, and has been involved in determining the GI of South African foods for more than two decades.

Marinda Venter


Marinda Venter is a registered dietitian who works part-time at a private practice in Nelspruit. She also works with the Glycemic Index Foundation of South Africa, writing product reports and newsletters.

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