Hard Belly

It sounds like your father may have metabolic syndrome. There is no standard diagnostic criteria, but the following is a list of criteria that many organizations use (metabolic syndrome present when 3 or more conditions met).
Waist circumference of more than 40" in men or more than 35" in women
BMI of 25 or higher
Fasting Triglyceride level of 150 mg/dL or higher
HDL level of less than 40 mg/dL in men or less than 50 mg/dL in women
Blood pressure of 130/85 mm Hg or higher
Fasting glucose level above 100mg/dL

Additional risk factors include the following:
Family history of type 2 diabetes
Hypertension
Coronary heart disease (CHD)
Polycystic ovary syndrome (PCOS)
Sedentary lifestyle
Advanced age

If he meets the criteria, metabolic syndrome correlates to pre-diabetes (which can lead to diabetes and heart disease). In my experience, diet and exercise are key to reversing this and reducing your dad's waist circumference (hard belly). His diet may be clean, but he also needs to balance his blood sugar with balanced, regular meals, the right breakfast, and regular exercise.
The step by step process I use to balance blood sugar for my clients is:
1. Determine diet direction and calculate the amount of protein they need for the day in grams to ensure they get enough each day.
2. Focus on breakfast. Nothing helps people feel better faster than eating a balanced meal of carbs (non-refined), fats, protein within 30-60 minutes of getting out of bed. You'll notice that sugar addicted clients may eat a fairly healthy lunch and dinner, but skip or eat an all-carb breakfast.
3. Next, you have their attention, because they're feeling better. Reduce the number of bread (refined flour bread, bagels, tortillas, pretzels, pasta, cookies, cake, crackers) servings per week to 8 depending on how sugar sensitive they are. You may have to do this s-l-o-w-l-y. You might start with 14 servings per week and then reduce from there. Offer them recipe ideas for meals without the bread. Substitute veggies to introduce Eating 4 Health.
4. All meals should be balanced: contain fats, protein and carbs. The ratio will be determined by you based on your Diet Direction recommendation for that client.
5. Eat regular meals: first breakfast, 3-4 hours later lunch, 3 hours later an "after-school" snack, and 3-4 hours later dinner. All meals should be on a plate, eaten seated at the table. Some with severe hypoglycemia may need a bedtime snack so their blood sugar doesn't get too low at night and interrupt their sleep.
6. Have them take a blood sugar balancing supplement (chromium, cinnamon, B vites are good ingredients) daily for support. Check them for other nutrient deficiencies: zinc, EFAs, B-vites, magnesium and other minerals and replace as needed.
7. Let them have a limited but reasonable amount of sweet treats, like one cookie, a piece of dark chocolate, etc, but make sure they eat it with or immediately after a meal and not by itself to keep blood sugar balanced. They won't be able to change their diet/habits if they're feeling restricted so reduce the frequency as you can. Soon, with their blood sugar balanced they won't have as many or as severe of sugar cravings. Alcohol can be an issue here too. If you're reducing their alcohol, so they're still drinking some, make sure they consume it only with a meal and not by itself. Alcohol LOWERS blood sugar, and in response people often overeat or binge after alcohol (even the next day) because their blood sugar is now spiking higher and bottoming out again in response, especially for those who are sensitive to alcohol and don't metabolize it well.
8. Many will need help with the sugar "habit." Therapeutically support them to ensure they have sweetness in other areas of their lives. How is their job, relationship, family life, self-care and confidence? Support here, in the form of therapy, helps with long-term goals.
9. Eating 4 Health. They're now ready to improve the quality and nutrient density of their diet for long-term health.
I implement these goals over the course of about 3-5 weeks depending my clients health and willingness, and then hope they follow the recommendations for regular eating indefinitely.

Oftentimes when people have had imbalanced blood sugar for some time (months or even years) it takes a while (weeks) of eating very regularly (every 3-4 hours) for their blood sugar to stop going so high and so low during the day. During this time of feeding themselves regularly to balance blood sugar, some people are very sensitive to refined carbohydrates (or even carbs from grains/fruits) and eating them even with a balanced meal can cause larger than normal spikes and valleys in blood sugar. So I recommend greatly reducing refined carbs, grains and fruits at meals with some people, especially at breakfast! People will say that they eat their oatmeal (refined) with nuts/seeds and maybe even some butter (and they're also adding maple syrup and banana). But the bulk of an oatmeal or grain cereal breakfast is still carbohydrates and may be too many carbs for those with blood sugar regulation issues, especially hypoglycemia. (Until they resolve blood sugar issue, then more grains/fruits can be reintroduced.)

Some people who have had imbalanced blood sugar for while and are hypoglycemic may also need to have a small, balanced snack before bed so their blood sugar doesn't get too low during the night or early morning hours. If you're waking up with very low blood sugar in the morning, and then eating a breakfast with carbohydrates, this can spike your blood sugar up higher than it would if your blood sugar is not very low at breakfast time. The people who have had imbalanced blood sugar for a while and are hyperglycemic need to add exercise into their routine to help pull those blood sugar numbers down.

I've also noticed with myself and my clients that when someone skips a meal or eats sweets one day, which causes ups and downs in their blood sugar, they often cannot recover balanced blood sugar right away even if they're eating regular, balanced meals. It may take a day or two to recover their balance and this is evident by many symptoms, including cravings for sweets or breads. This is why it can be so devastating to people who are trying to avoid sugar/refined carbs or trying to lose weight when they make a mistake on one day. They will often suffer the ill effects of that one day for a couple of days.

So for the sake of balancing your blood sugar to get beyond the cravings, I would suggest a balanced snack (some carbohydrate (veggies), protein and fat) if you're feeling hungry and in the meantime reducing the refined carbohydrates, glycemic fruits and sugars in your diet. I also recommend people drink WATER first when they're hungry to make sure they aren't really THIRSTY. If they're still hungry after drinking water, then have the balanced snack.

Good luck with your dad!