When fully understanding MT you must be aware that typing evolves across a spectrum, and that an individual can be one "type" at one point in the day and shift "types" throughout the day.
Metabolic typing relies on the individual to complete a questionnaire based upon their reactions to food. The problem occurs that people frequently have an adgenda in that they assume certain foods are "good" and others are "bad." They come ready conditioned and answer as such. From those fully ingrained, (theirs a pun there) in the grain is healthy, meat is bad camp, that are more likely to be a carb type. To the people who've suddenly realised that they suffer blood sugar issues and end up in the "protein" is king camp.
As such they answer the questions to suit their conditioning. Several times in my clinical experience I've seen people blatantly ignore cold hard evidence, in favor of picking the answers that suit what they believe. This doesn't mean clients or practitioners are falsifying facts. It just means that they are falling foul of missing the evidence and are relying on answers from an individual that is pre conditioned. Be aware that the answers you select have an element of conditioning to what you regard is correct.
This doesn't mean MT is useless, its a fantastic tool to encourage people to combine fats, protein and carbohydrate. Is it healthy for someone to restrict themselves to a minimal range of fruits and veg, purely on the basis that they have conditioned themselves to believe they can't cope with it? In fact if they can't handle potato should we leave them on a limited diet or should we be working to get them fully functional no matter what they consume (as long as its natural).
When I take a client on I use MT to assess where they believe they are, from that point I set about understanding various physiological effects within the body and educate them about how to correct the endocrine system to full function. Theirs nothing better than seeing a client return to the freedom of their childhood with an ability to eat freely and move without pain or fatigue.
The clients (or you if your working on yourself) opinion matters so I fully believe it is important to listen to what the client tells you about themselves. The MT questionnaire is a fantastic tool for recording this but it is not conclusive data. As practitioners we have to realise that we have a broad range of tests at our disposal to build a full picture of a clients physiology. If we fail to use this we are simply twisting the facts to meet our pre determined theory.
Test everything you possibly can and leave no stone unturned. Do I still use MT? Yes I do and to a degree I will always use it. However it has serious limitations, how do I know? Having worked with it and tested it myself for 4 years following it 100%, the results didn't match the commitment I put in. Use MT for what it is, one tool in the box of tricks to coach a client to health.