OK! Let's talk Liquid Nutrition!!
This is a favorite subject of mine actually so this post might get rather long, but it is with the intent to shed light and help!
Now I was PEG dependent for 18 months before I really started trying solid foods, even now the lions share of my nutrition is liquified, either blended, juiced or Ensure as due to my swallow issues I'm unable to eat enough solids to maintain a "healthy" weight.
Before cancer I was a tank of a guy, 5'9" on a good day and 210 lbs and in good shape from lifting weights, wrestling and running etc... I lost a total of 70 lbs during treatment and after surgery, leaving me wasted and weakened and a scrawny 140 lbs. When I needed to gain weight and build myself back up, I found that without the ability to eat most solids getting back to optimum weight and putting on good muscle was going to be a challenge, which is fine because I rather like challenges.
Nutrition for your brother is "vital" or to translate in Spanish "Muy Importante!" clap clap clap! Cancer and the bodies own immune response puts the cancer patient into a hypermetabolic state where they burn through calories and macro nutrients (fat,protein, carbohydrates) at an alarming rate and due to certain hormone responses nutrition "uptake" slows. Coupled with limited intake this all sets the stage for "cachexia" or cancer related "wasting" syndrome, basically why cancer patients get scary skinny really quick, which adds to a poorer prognosis.
So! What can be done you ask?!?! Thankfully "mucho" or "much" for those non Spanish speaking individuals out there!
Ensure Plus is a great start, has all of the essential vitamins and minerals for complete nutrition and is usually what's recommended for "interim" sole source feeding. It's 350 calories per bottle with 11 g's (grams) of Fat, 50g Carbohydrates, and 13g's of Protein.
Now there are several survivors on these forums that recommend Carnation Instant Breakfast VHC (very high calorie) it's 560 calories per can, 30.6gs fat, 49.2gs Carbohydrates, 22.5gs protein and a product I would consider a good start as well.
Here's the issue though with using just these products alone, "very low"(Ensure is 15% protein, VHC is 16%) on protein which is vital as his body is fighting and recovering. In fitness training for athletes there is a term called the "Golden Ratio" of Fat, Carbs & Proteins that top athletes in training (ratio varies slightly depending on the type of training they do and sex of athlete)use as a rule to fuel their bodies optimally. The ratio (again depending on the training) is 40-50% of calories from Carbs, 20-30% fat, 20-30% protein. For men looking to build or maintain muscle, the fat and protein portions are a vital area to stick, even more so in the cancer patient as per this article (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311497/
In cancer patients there is a shift in use of nutrients in the body (caused by hormones) from building and maintenance to the immune response resulting in increased rate of muscle protein degradation and increase in acute-phase protein synthesis, with progressive depletion of lean body mass. This basically means that your body is breaking down it's own muscle into amino acids which it then uses in other areas,robbing Peter to pay Paul in other words. In general weight loss and lower percentage of lean muscle mass "is a major prognostic indicator of poor survival and impaired response to anti-neoplastic therapy."
So supplementing either of the above two choices with a Protein Powder is just good sense, I recommend Whey Protein as it has the fastest uptake of all the other kinds of protein out there which is why it's preferred by elite athletes and trainers.
As a guy it's also important to keep testosterone in the body up, which is difficult during treatment due to stress, and many of the drugs usually prescribed to cancer patients constrain testosterone production in the body (antidepressants, pain killers etc..) so it's important to make sure he's getting enough "fat" in his diet. In guys the higher percentage of fat in the blood increases testosterone in the body which is key to muscle maintenance, mood stabilizing etc.. Testosterone is arguably our most important hormone. For this reason I'd choose the Carnation VHC, roughly 50% of it's calories come from fat, in the form of Canola Oil which is considered very healthy due to it's low saturated fat content (lower than Extra Virgin Olive Oil).
You can get 24 cans of it through Amazon (use the OCF Link!!) for $31. I'd also recommend Cytosport's 100% Whey Protein Powder which is what I use, is also available on Amazon.
If you go with the Ensure, or Boost etc, have them mix it with a tablespoon of Canola Oil (120 calories & 14g fat per "tablespoon") and a scoop of Protein powder. I'd also say your brothers calorie intake is going to depend on his size, however I'd say at least 2600 calories per day, but personally I'd try for 3000-3500.
Good luck, I hope this helped, sorry for the novel!