I believe your family member is an example that Barry Sears, Loren Cordain and
on the more extreme side, Robert Atkins and Michael/Mary Eades, are correct.

This is because he is following a high carbohydrate, low protein, low fat diet.

(All the following ratios are in the format carbohydrates:protein:fats.)

Such a diet is probably quite close to that recommended by the American Heart
Association in a 55:30:15 ratio, disastrous for diabetics.

To lower his blood sugar and cholesterol, he should start on Sear's Zone Diet,which
is basically a lower carbohydrate, moderate protein and higher fat in a 40:30:30 ratio,
or Cordain's Paleo Diet - low carbohydrate, moderate protein, high fat, typcally as 15:30:55.

Robert Atkins doesn't specifyl ratios for his diet, but his followers go on very low
carbohydrate, moderate protein, very high fat (typically 5:25:70) diet, while Michael
and Mary Eades' proponents go for very low carbohydrate, very high protein and
medium fat. Atkins' and Eades' diets are actually a weight loss diets.

Loren Cordain's hunter-gatherer Paleo Diet is also more moderate, feasible and
safer than Atkin's. He doesn't specifiy fixed ratios, but followers typically apportion
15:30:55 for carbs, protein and fats.
" A very low-carbohydrate, ketogenic diet was the standard treatment for diabetes
throughout the 19th century. "

http://en.wikipedia.org/wiki/Low-carbohydrate_diet

http://en.wikipedia.org/wiki/Paleolithic_diet
http://thepaleodiet.com

http://board.crossfit.com/showthread.php?t=54614
https://www.zonediet.com/
http://www.atkinsdietbulletinboard.com/

http://forum.lowcarber.org/showthread.php?t=374787
http://www.eatprotein.com/

http://www.proteinpower.com
Read their books -

Barry Sears - The Zone: A Dietary Road Map
Robert Atkins - Dr Atkins' New Diet Revolution
Michael and Mary Eades - Protein Power
The Atkins Diet is actually quite close to the ketogenic diet for controlling epilepsy.

http://en.wikipedia.org/wiki/Ketogenic_diet#Modified_Atkins
Here's your proof. The diet closest to the one in this study (20:30:50)
would be Cordain's Paleo.

Effect of a High-Protein, Low-Carbohydrate Diet on Blood Glucose Control
in People With Type 2 Diabetes.

http://diabetes.diabetesjournals.org/content/53/9/2375.full
Very low carbohydrate, very high protein diet (8:69:23) prevents/fights cancer.
That closest to this would be Eades' Protein Power diet.

A Low Carbohydrate, High Protein Diet Slows Tumor Growth and
Prevents Cancer Initiation.

http://cancerres.aacrjournals.org/content/71/13/4484.full