Type 3 Diabetes – (Less) Food For Thought?

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As both prediabetes and diabetes increase at astronomical rates, new research shows the direct link between sugar imbalance and Alzheimer’s disease (AD). Doctors are taught that diabetes can adversely affect the kidneys, cardiovascular and nervous systems. One organ that gets less attention when it comes to poor glycemic control is the brain. Research confirms that increased body mass index and diabetes, which are the result of a high-carbohydrate diet, have been linked to AD, the most common form of dementia.

A recent study has clarified this phenomenon. Fifty healthy subjects (mean age 60) were divided into one of three groups: 30% calorie restriction, 20% increase in omega-3 fatty acid intake, or no diet change. A striking conclusion from this small but important study was that the calorically restricted group had a significant 20% improvement in verbal memory (1). In addition, after 3 months, it was found that weight, fasting insulin levels, and highly sensitive C-reactive protein levels (a marker of inflammation in heart tissue) decreased only in the calorie-restricted group, but not in the other two groups.

It should be brought to light that the FDA would probably have approved any drug that promised a 20% improvement in verbal memory. Changing your diet can be a surefire way to achieve the same goal. Physicians and nutritionists should strongly consider incorporating the results of this study into the dietary counseling of AD patients. A healthy diet is not only good for the heart, but also for the brain.

The above research has its roots in a landmark study called the Rotterdam Study, published in the journal Neurology (2) in 1999. The study showed that diabetes mellitus almost doubled the risk of AD. The novel term “type 3 diabetes” links insulin resistance to AD.

In type I diabetes, there is a lack of insulin production, resulting in patients having to resort to insulin injections to regulate glucose levels. In type II diabetes, there is resistance at the cellular level to the insulin produced. These patients require a strict, low-glycemic index diet and medication as needed. Poorly controlled type II diabetes sometimes also requires insulin. Type 3 diabetes shares elements of both type 1 and type 2 diabetes in that there is both a decrease in insulin production and resistance to insulin receptors.

Type 3 diabetes was discovered in 2005 by Dr. Suzanne de la Monte, a neuropathologist at Brown Medical School (3). dr de la Monte and her team studied postmortem brain tissue from patients suffering from AD and found that AD may actually be a neuroendocrine disorder linked to insulin signaling.

In addition to regulating blood sugar levels, insulin acts as a growth factor for all cells, including neurons in the brain. Insulin resistance or insulin deficiency contributes to degenerative processes in the brain (4).

A group of researchers at Northwestern University found the likely mechanism behind why AD brains are both insulin-deficient and insulin-resistant. according to dr William Klein, who led the research, a neurotoxic molecule called ADDL (amyloid beta-derived diffusible ligand) could be responsible for the phenomenon. ADDLs help explain why Alzheimer’s patients have low insulin levels and insulin resistance in their brains.

In healthy brains, insulin binds to a receptor at a synapse, a specialized junction that connects cells, allowing them to communicate with each other. Once this occurs, a mechanism is initiated that allows for the formation of memories. The team of dr. However, Klein found that ADDLs interfere with this communication mechanism (5). ADDLs bind to the synapses and change their shape. Because their shapes are altered, insulin cannot bind to the synapses as efficiently as it normally would. This in turn makes the cells insulin resistant, as in type II diabetes.

Proactively applying this constellation of new medical research is critical, especially when the intervention is benign. Neglecting to recommend simple dietary changes to an AD patient can be potentially harmful and lead to rapid cognitive decline. Diet and other lifestyle changes should not be overlooked when treating Alzheimer’s disease.

References:

1. Witte AV et al. Calorie restriction improves memory in the elderly. Proc Natl Acad Sci USA 2009 Jan 27;106:1255.

2. A Ott et al., Diabetes and the risk of dementia: Rotterdam Study, Neurology 1999; 53:1937

3. de la Monte, Journal of Alzheimer’s Disease, March 2005

4. Li L, Holscher C. Common pathologic processes in Alzheimer’s disease and type 2 diabetes: a review. Brain Res Rev. 2007 Dec;56(2):384-402. Epub September 11, 2007

5. Brain Affected by Alzheimer’s Disease: The Presence of Oligomeric Aβ Ligands (ADDLs) Suggests a Molecular Basis for Reversible Memory Loss (Gong Y et al, PNAS, 2003)

Thanks to Zina Kroner

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