Following a protein restricted diet requires patients with MSUD to avoid certain foods, but sometimes avoiding these foods leads to avoiding other important nutrients. An example of this is essential fatty acids.

Essential fatty acids are fats that we must obtain in our diets because our bodies cannot make them. Commonly referred to as omega-3 and omega-6 fats, these nutrients are important for many functions in our bodies, including the formation of healthy skin cells and other cell membranes, brain development, and the achievement of optimum vision. In fact, the brain and retina contain very high amounts of omega-3 and omega-6 fatty acids, which demonstrate their importance in these tissues. Omega-3 fats have also been shown to have help protect against heart disease.

Many types of omega-3 and omega-6 fatty acids exist. Fortunately, the body has the ability to use the essential fatty acids alpha-linolenic acid (in the omega-3 family) and linoleic acid (in the omega-6 family) to make the other omega-3 and omega-6 fatty acids. Alpha-linolenic acid (ALA), which is found in nuts, flaxseed and canola oils, can be converted to other important omega-3 fats like eicosapentanoic acid (EPA) and docosahexanoic acid (DHA), in small amounts. Linoleic acid (LA), found in corn, sunflower, and safflower oils, can be converted to the omega-6 fatty acid referred to as arachidonic acid (AA) as well as other omega-6 fats.

A recent evaluation of a small group of patients with Maple Syrup Urine Disease showed that the plasma levels of DHA were significantly lower in MSUD patients than in similar individuals without MSUD (submitted for publication). There was no difference in the plasma levels of the essential omega-3 fatty acid ALA between MSUD patients and those without MSUD. The normal ALA levels and low DHA levels in this small number of MSUD patients raises the question about adequate fat intake. Other studies have shown that plasma DHA levels fluctuate to reflect dietary intake, so the lower levels in MSUD patients reflect a lower intake of DHA. More research is needed with more subjects to evaluate essential fatty acid intake from diet and the choice of medical food.

So in the meantime, what can we eat to make sure we are getting these essential fatty acids in our diets? Omega-6 fats are easily obtained in the diet through corn, safflower, and sunflower oils and should be adequate in MSUD diets where these plant oils are not restricted. The omega-3 fats are more of a challenge to include in the diet. ALA is found in canola and soy oils, which are easily available in marketplaces. Other more expensive sources of ALA include walnut and flaxseed oils; DHA and EPA are found in fatty fish or fish oils. Obviously, fish and nuts are not allowed in MSUD diet, but soy or canola oil can be added to the MSUD diet.

Ongoing clinical monitoring of plasma levels is used to establish adequacy of essential fatty acids in patients with MSUD. Further studies will clarify if supplementation with DHA and EPA ("fish oil" capsules) is needed. Nonetheless, paying attention to total and essential fatty acid intake in the MSUD diet is important for optimum development. Ask your dietitian to calculate total fat and essential fatty acid intake for your diet. Fatty acid data for different foods are available on:

 Source Amount (5ml)
 Linoleic acid (mg)
 Linolenic acid (mg)
 Canola oil
 1 tsp 915 420 40
 Corn oil
 1 tsp 241 50 40
 Safflower oil
 1 tsp 3360 0 40
 Soy oil
 1 tsp 2295 305 40
 Walnut oil
 1 tsp 2380 470 40
 Flax oil
 1 tsp 570 2400 40

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