Other then potential short length of New to Weight Training gaines, IMO, no fitness training will be able to overcome a "bad diet".
And, I am not fixing a "normal" definition to the term "bad diet".
Most knowledgable persons in diet and fitness training would probably know what I am referring to.
Alot of persons do not understand (or attempt to gain knowledge of) the metabolic adaptions that "can" take place within ones body, and become confused, disheartened, and disgusted, with results in the attempt to earn their fitness goals.
When the body tries to makes muscle, it "can be" metabolically "expensive", as bodily adaptions are taking place.
When the body tries to lose tissue, it "can be" metabolically "expensive", and likewise bodily adaptions are taking place.
To lose tissue "some type of deficit is REQUIRED". This is can be done through a reduction (manipulation) in calories AND reduction (or manipulation) of three main nutrients (Carbs, Proteins, and Fats).
For example:
Using a calorie deficit or a traditional one-way approach method:
For sake of arguement, one cuts calories 20% from their approximated MT-Line. The persons "weight" starts to drop.
As the weight drops, so does one's metabolic rate (and potential caloric needs). No way around it. And, the opposite is true in gaining "weight".
At this point, you could cut calories again to trigger another deficit based off of your NEW maintenance level.
At some point though, one can't keep cutting calories, IMO.
If you do, the weight loss will eventually slow or stop, IMO.
If it doesn't, it is going to leave you with a VERY inefficient metabolism, IMO. (and can be one the body will "eventually" not overcome, when speaking in terms of longated severe deficits)
If you have already ignited the stoppage, it is time to "smartly" manipulate your calories to reverse the physiological survival mechanisms one just fired up.
This is my opinion of course, and I have used this thought process with MUCH SUCCESS.
In a "severely deficient calorie deficit" (EVEN WITH weight training), one will "increase the odds" that the body will dine on more muscle than the unwanted fat. Yes, the weight training prevents it from being worse, but the margin of the calorie deficit, in this example, is the GREATER evil.
The ALMIGHTY Calorie is KING in muscle gain or fat loss, and one can use the "nutrients" to a manipulative advantage. This is WHY I PRESS educating oneself. So many hardships and depression can be prevented just through taking the necessary time.
I will end this post here. Its NOT exhaustive and a little short, I know. However, with what I said thus far, what do YOU think the answer is?
Note: Be careful with the definition of "bad diet". For example, one can lose fat tissue having less then optimal diet (such as eating twinkies once in a while-assuming nondiabetic, and healthy internally) if the correct calorie deficit is present particular to the person.
Best regards,
Chillen