My uncle recently read my handout and says he is following a primal/low carbohydrate diet for the past 10 days but he has not lost any weight. He is obese and has diabetes controlled well on Byetta--probably a good but very expensive way to control diabetes!! In addition giving him some diet reminders and telling him to decrease fruit consumption and maybe even counting carbohydrate grams, his question to me was, "Should I stop Byetta?"
I think Byetta has minimal positive metabolic effects If you are on a low carbohydrate diet and you don't really need the extra kick in the pancreas response to control blood sugars.
Byetta is a great medication when diabetics or pre-diabetics are eating the average diet containing 50-60% calories from carbohydrates though.
The positive effects that would lead to weight loss though are either not needed or can be regulated without Byetta on a low carb diet. The positive effects that would lower blood sugar aren't needed if the sugar can be controlled on a low carb diet. Byetta does increases satiety (delays gastric emptying) and decreases appetite/satiety via the effect on thalamic receptors--but a fat and protein rich meal can also increase satiety and relieve hunger.
Byetta will make the pancreas more sensitive to blood sugar and cause a much higher and quicker release of insulin. By suppressing glucagon release, Byetta stops glycogen in the liver from breaking down into glucose (and discourages the new storage of glucose as glycogen in the liver). The greater pancreatic sensitivity to blood sugar (and thus insulin release) that Byetta gives though is helpful if you have a "burnt out" pancreas. It will lead to a quicker control of blood sugar and the appropriate timing of the insulin release. This beneficial in those advanced diabetes--those with a "burnt out" pancreas with severe dysfunction.
Byetta may not help much on a low carbohydrate diet if you don't have fairly advanced diabetes. Unless you really need Byetta to control (by enhancing insulin secretion) even the small rise in blood sugar that occurs with a low carbohydrate diet, it seems plausible that this would lead to higher insulin levels than are needed to decrease blood sugars and prevent the toxicity of high blood sugars. Higher insulin levels even with a normal blood sugar will lead to less lipolysis (net fat storage). If you have pre-diabetes or easily controlled diabetes (hemoglobin A1c < 7.5 on Byetta and/or metformin), changing from a conventional high carb diet to a low carb diet will likely lead to at least as much benefit as Byetta. It is my opinion that Byetta may not improve blood sugars or lead to more weight loss when added to a low carbohydrate diet unless the patient's diabetes is advanced.
I'd welcome comments from patients and doctors on the additive benefits of Byetta to a low carbohydrate diet, if any.